Reverse forwarding information base enforcement

ABSTRACT

In exemplary embodiments of the present invention, a router determines whether or not to establish a stateful routing session based on the suitability of one or more candidate return path interfaces. This determination is typically made at the time a first packet for a new session arrives at the router on a given ingress interface. In some cases, the router may be configured to require that the ingress interface be used for the return path of the session, in which case the router may evaluate whether the ingress interface is suitable for the return path and may drop the session if the ingress interface is deemed by the router to be unsuitable for the return path. In other cases, the router may be configured to not require that the ingress interface be used for the return path, in which case the router may evaluate whether at least one interface is suitable for the return path and drop the session if no interface is deemed by the router to be suitable for the return path.

This application is a continuation of U.S. patent application Ser. No.17/305,985, filed Jul. 19, 2021, which is a continuation of U.S. patentapplication Ser. No. 15/169,003, filed May 31, 2016, the entire contentof which is herein incorporated by reference.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This patent application is related to U.S. patent application Ser. No.14/497,954 filed Sep. 26, 2014, entitled, “NETWORK PACKET FLOWCONTROLLER,” the disclosure of which is incorporated herein, in itsentirety, by reference.

This patent application also is related to U.S. patent application Ser.No. 14/562,917, filed Dec. 8, 2014, entitled, “STATEFUL LOAD BALANCINGIN A STATELESS NETWORK,” the disclosure of which is incorporated herein,in its entirety, by reference.

This patent application also is related to U.S. patent application Ser.No. 14/715,036, filed May 18, 2015, entitled, “NETWORK DEVICE AND METHODFOR PROCESSING A SESSION USING A PACKET SIGNATURE,” the disclosure ofwhich is incorporated herein, in its entirety, by reference.

This patent application also is related to U.S. patent application Ser.No. 14/963,999, filed Dec. 9, 2015, entitled, “ROUTER WITH OPTIMIZEDSTATISTICAL FUNCTIONALITY,” the disclosure of which is incorporatedherein, in its entirety, by reference.

This patent application also is related to U.S. patent application Ser.No. 14/833,571, filed Aug. 24, 2015, entitled, “Network Packet FlowController with Extended Session Management,” the disclosure of which isincorporated herein, in its entirety, by reference.

This patent application also is related to U.S. patent application Ser.No. 15/054,781, filed Feb. 26, 2016, entitled, “NAME-BASED ROUTINGSYSTEM AND METHOD,” the disclosure of which is incorporated herein, inits entirety, by reference.

This patent application is also related to U.S. patent application Ser.No. 15/168,877, filed May 31, 2016, entitled “LINK STATUS MONITORINGBASED ON PACKET LOSS DETECTION,” the disclosure of which is incorporatedherein, in its entirety, by reference.

TECHNICAL FIELD

The present invention relates to data routing and, more particularly, toreverse forwarding information base enforcement in a communicationsystem.

BACKGROUND

The Internet Protocol (“IP”) serves as the de-facto standard forforwarding data messages (“datagrams”) between network devices connectedwith the Internet. To that end, IP delivers datagrams across a series ofInternet devices, such as routers and switches, in the form of one ormore data packets. Each packet has two principal parts: (1) a payloadwith the information being conveyed (e.g., text, graphic, audio, orvideo data), and (2) a header, known as an “IP header,” having theaddress of the network device to receive the packet(s) (the “destinationdevice”), the identity of the network device that sent the packet (the“originating device”), and other data for routing the packet.

Many people thus analogize packets to a traditional letter using firstclass mail, where the letter functions as the payload, and the envelope,with its return and mailing addresses, functions as the IP header.

Current Internet devices forward packets one-by-one based essentially onthe address of the destination device in the packet header in accordancewith an Internet routing protocol such as BGP, OSPFv2, IS-IS, etc. Amongother benefits, this routing scheme enables network devices to forwarddifferent packets of a single datagram along different routes to reducenetwork congestion, or avoid malfunctioning network devices. Thoseskilled in the art thus refer to IP as a “stateless” protocol because,among other reasons, it does not save packet path data, and does notpre-arrange transmission of packets between end points.

Current Internet routing protocols generally cannot route packets froman element in one private network to an element in another privatenetwork because the IP address spaces used for elements in those privatenetworks often overlap. These are often referred to as “unroutable”addresses, which are not useful on the public Internet.

Therefore, Network Address Translation (NAT) is often used to convertbetween local addresses used for routing within the private networks andpublic Internet addresses used for routing over the public Internet. Thepublic Internet address is used to route packets between the privatenetworks. Within each private network, other information in the packetis used to determine the local address used to route the packet to thedestination entity within the destination private network.

Over the past decade, network challenges have evolved from bandwidth andbroadband availability to security and mobility. Cloud has emerged as aprimary service delivery architecture that achieves economies of scaleunheard of in the past. Cloud embraces sharing of resources, includingcomputing and storage. This has created a huge number of newrequirements unmet by today's IP routing models, such as:

-   -   Private-network to private-networking models    -   Dynamically-arranged, service-specific Quality of Service    -   Unified IPv4 and IPv6 routing tables    -   Authenticated directional routing    -   On-the-fly encryption    -   Overlapping address support    -   Load balancing instead of equal-cost multipath (ECMP)    -   Integrated DPI and resulting flow analytics

To meet these requirements, current architectures require middleboxes(e.g., firewalls, DPI devices, load balancers) mixed with overlaynetworking (e.g., VLANs, nested VLANs, VxLANs, MPLS, Cisco ACI, VMwareNSX, Midonet) and orchestration (e.g., OpenStack, service functionchaining).

SUMMARY

In accordance with one embodiment, a method of managing stateful routingsessions by a router involves receiving, by the router, a first packetfor a new stateful routing session on an ingress interface of therouter; analyzing, by the router, at least one candidate interface forsuitability for a return path for the session; when at least onecandidate interface is a suitable candidate interface for the returnpath for the session, establishing the stateful routing session using asuitable candidate interface for the return path for the session; andwhen no candidate interface is a suitable candidate interface for thereturn path for the session, dropping the session.

In accordance with another embodiment, a router comprises a plurality ofcommunication interfaces, a computer storage, and a packet routerconfigured to implement method of managing stateful routing sessionsinvolving receiving, by the packet router, a first packet for a newstateful routing session on an ingress interface of the router;analyzing, by the packet router, at least one candidate interface forsuitability for a return path for the session; when at least onecandidate interface is a suitable candidate interface for the returnpath for the session, establishing the stateful routing session using asuitable candidate interface for the return path for the session; andwhen no candidate interface is a suitable candidate interface for thereturn path for the session, dropping the session.

In accordance with another embodiment, a computer program productcomprising a tangible, non-transitory computer readable medium hasembodied therein a computer program that, when run on at least onecomputer processor, implements a packet router for a router, the packetrouter implementing a method of managing stateful routing sessions by arouter involving receiving a first packet for a new stateful routingsession on an ingress interface of the router; analyzing at least onecandidate interface for suitability for a return path for the session;when at least one candidate interface is a suitable candidate interfacefor the return path for the session, establishing the stateful routingsession using a suitable candidate interface for the return path for thesession; and when no candidate interface is a suitable candidateinterface for the return path for the session, dropping the session.

In various alternative embodiments, the at least one candidate interfacemay consist of the ingress interface. In other embodiments, the at leastone candidate interface may comprise the ingress interface and/or atleast one interface other than the ingress interface. In someembodiments, when a plurality of candidate interfaces are suitablecandidate interfaces, one of the suitable candidate interfaces may beselected for return path for the session. Analyzing at least onecandidate interface for suitability for a return path for the sessionmay involve maintaining a reverse forwarding information database thatstores performance information for each router interface and referencingthe reverse forwarding information database to determine suitability.The at least one candidate interface may include a plurality ofcandidate interfaces, in which case analyzing at least one candidateinterface for suitability for a return path for the session may involvereferencing the reverse forwarding information database to determine abest suitable candidate interface from among the plurality of candidateinterfaces.

Additional embodiments may be disclosed and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Those skilled in the art should more fully appreciate advantages ofvarious embodiments of the invention from the following “Description ofIllustrative Embodiments,” discussed with reference to the drawingssummarized immediately below.

FIG. 1 schematically shows a hypothetical prior art network that mayimplement certain illustrative embodiments of the invention;

FIG. 2 schematically illustrates a prior art technique for fragmenting amessage;

FIG. 3 schematically shows a hypothetical internet that may implementcertain illustrative embodiments of the invention;

FIG. 4 schematically shows relevant portions of a router including aforwarding path and a service path, in accordance with one exemplaryembodiment;

FIG. 5 schematically shows additional details of shared management of arouting table by the forwarding path and the service path of FIG. 4 , inaccordance with certain illustrative embodiments.

FIG. 6 is a schematic diagram of an action chain used to process andforward packets, in accordance with one exemplary embodiment.

FIG. 7 schematically shows a hypothetical internet that includesconventional routers and augmented IP routers (AIPRs), in accordancewith one exemplary embodiment.

FIG. 8 schematically shows an example of lead packet processing from asource node to a destination node for stateful routing, in accordancewith one exemplary embodiment.

FIG. 9 is a schematic diagram showing session-related data associatedwith a first waypoint AIPR based on the lead packet processing of FIG. 8, in accordance with one exemplary embodiment.

FIG. 10 is a schematic diagram showing session-related data associatedwith an intermediate waypoint AIPR based on the lead packet processingof FIG. 8 , in accordance with one exemplary embodiment.

FIG. 11 is a schematic diagram showing session-related data associatedwith a final waypoint AIPR based on the lead packet processing of FIG. 8, in accordance with one exemplary embodiment.

FIG. 12 is a schematic diagram providing an example of session packetprocessing for an example packet sent from the source device to thedestination device through the AIPR devices for the session establishedin FIG. 8 , in accordance with one exemplary embodiment.

FIG. 13 is a schematic diagram providing an example of session packetprocessing for a return packet sent by the destination device to thesource device through the AIPR devices for the session established inFIG. 8 , in accordance with one exemplary embodiment.

FIG. 14 is a flowchart schematically illustrating some lead packetprocessing operations performed by an AIPR, in accordance with oneexemplary embodiment.

FIG. 15 is a flowchart schematically illustrating some session packetprocessing operations performed by an AIPR, in accordance with oneexemplary embodiment.

FIG. 16 schematically shows a layout of an Ethernet header, identifyingfields used for identifying a beginning of a session, in accordance withone exemplary embodiment.

FIG. 17 schematically shows a layout of an IP header, identifying fieldsused for identifying a beginning of a session, in accordance with oneexemplary embodiment.

FIG. 18 schematically shows a layout of a TCP header, identifying fieldsused for identifying a beginning of a session, in accordance with oneexemplary embodiment.

FIG. 19 schematically shows a block diagram of an AIPR of FIG. 7 , inaccordance with one exemplary embodiment.

FIG. 20 shows a schematic illustration of information stored in aninformation base by the AIPR of FIGS. 7 and 19 , in accordance with oneexemplary embodiment.

FIG. 21 schematically shows a modified lead packet produced by the AIPRof FIGS. 7 and 19 , in accordance with one exemplary embodiment.

FIG. 22 is a flowchart illustrating some of the operations performed bythe AIPR of FIGS. 7 and 19 , in accordance with one exemplaryembodiment.

FIG. 23 is a flowchart illustrating some of the operations involved withforwarding a lead packet as part of the process of FIG. 22 , inaccordance with one exemplary embodiment.

FIG. 24 is a flowchart for first session packet processing, inaccordance with one exemplary embodiment.

FIG. 25 is a flowchart for “bi-flow required” processing pursuant toFIG. 24 , in accordance with one exemplary embodiment.

FIG. 26 is a flowchart for “bi-flow not required” processing pursuant toFIG. 24 , in accordance with one exemplary embodiment.

FIG. 27 is a flowchart for “bi-flow not required” processing pursuant toFIG. 24 , in accordance with one alternate exemplary embodiment.

FIG. 28 is a schematic diagram of a reverse forwarding information base,in accordance with one exemplary embodiment.

FIG. 29 is a flowchart for determining if an ingress interface issuitable for a return path, in accordance with one exemplary embodiment.

DETAILED DESCRIPTION

In exemplary embodiments of the present invention, a router determineswhether or not to establish a stateful routing session based on thesuitability of one or more candidate return path interfaces. Thisdetermination is typically made at the time a first packet for a newsession arrives at the router on a given ingress interface. In somecases, the router may be configured to require that the ingressinterface be used for the return path of the session, in which case therouter may evaluate whether the ingress interface is suitable for thereturn path and may drop the session if the ingress interface is deemedby the router to be unsuitable for the return path. In other cases, therouter may be configured to not require that the ingress interface beused for the return path, in which case the router may evaluate whetherat least one interface is suitable for the return path and drop thesession if no interface is deemed by the router to be suitable for thereturn path.

Networks

Illustrative embodiments preferably are implemented within an otherwiseconventional computer network that uses common networking devices andprotocols. Among other things, a network includes at least two nodes andat least one communication link between the nodes. Nodes can includecomputing devices (sometimes referred to as hosts or devices) androuters. Computers can include personal computers, smart phones,television “cable boxes,” automatic teller machines (ATMs) and manyother types of equipment that include processors and network interfaces.Links can include wired and wireless connections between pairs of nodes.In addition, nodes and/or links may be implemented completely insoftware, such as in a virtual machine, a software defined network, andusing network function virtualization. Many networks include switches,which are largely transparent for purposes of this discussion. However,some switches also perform routing functions. For the presentdiscussion, such routing switches are considered routers. Routers aredescribed below.

A node can be directly connected to one or more other nodes, each via adistinct communication link. For example, FIG. 1 schematically shows aNode A directly connected to Node B via Link 1. In a given network(e.g., within a local area network), each node has a unique networkaddress to facilitate sending and receiving data. A network includes allthe nodes addressable within the network according to the network'saddressing scheme and all the links that interconnect the nodes forcommunication according to the network's addressing scheme. For example,in FIG. 1 , Nodes A-F and all the links 1-8 together make up a network100. For simplicity, a network is depicted as a cloud or as beingenclosed within a cloud. Absence of a cloud, however, does not mean acollection of nodes and links are not a network. For example, a networkmay be formed by a plurality of smaller networks.

Nodes can initiate communications with other nodes via the network, andnodes can receive communications initiated by other nodes via thenetwork. For example, a node may transmit/forward/send data (a message)to a directly connected (adjacent) node by sending the message via thelink that interconnects the adjacent nodes. The message includes thenetwork address of a sending node (the “source address”) and the networkaddress of an intended receiving node (the “destination address”). Asending node can send a message to a non-adjacent node via one or moreother intervening nodes. For example, Node D may send a message to NodeF via Node B. Using well known networking protocols, the node(s) betweenthe source and the destination forward the message until the messagereaches its destination. Accordingly, to operate properly, networkprotocols enable nodes to learn or discover network addresses ofnon-adjacent nodes in their network.

Nodes communicate via networks according to protocols, such as thewell-known Internet Protocol (IP) and Transmission Control Protocol(TCP). The protocols are typically implemented by layered softwareand/or hardware components, such as according to the well-knownseven-layer Open System Interconnect (OSI) model. As an example, IPoperates at OSI Layer 3 (Network Layer), while the TCP operates largelyat OSI Layer 4 (Transport Layer). Another commonly used Transport Layerprotocol is the User Datagram Protocol (UDP). Each layer performs alogical function and abstracts the layer below it, therefore hidingdetails of the lower layer. There are two commonly-used versions of IP,namely IP version 4 (“IPv4”) and IP version 6 (“IPv6”). IPv4 isdescribed in IETF RFC 791, which is hereby incorporated herein byreference in its entirety. IPv6 is described in IETF RFC 2460, which ishereby incorporated herein by reference in its entirety. The mainpurpose of both versions is to provide unique global computer addressingto ensure that communicating devices can identify one another. One ofthe main distinctions between IPv4 and IPv6 is that IPv4 uses 32-bitsource and destination IP addresses, whereas IPv6 utilizes 128-bitsource and destination IP addresses. TCP is described generally in IETFRFC 793, which is hereby incorporated herein by reference in itsentirety. UDP is described generally in IETF RFC 768, which is herebyincorporated herein by reference in its entirety.

For example, a Layer 3 message may be fragmented into smaller Layer 2packets if Layer 2 (Data Link Layer) cannot handle the Layer 3 messageas one transmission. FIG. 2 schematically illustrates a large message200 divided into several pieces 202, 204, 206, 208, 210 and 212. Eachpiece 202-212 may then be sent in a separate packet, exemplified bypacket 214. Each packet includes a payload (body) portion, exemplifiedby payload 216, and a header portion, exemplified at 218. The headerportion 218 contains information, such as the packet's source address,destination address and packet sequence number, necessary or desirablefor: 1) routing the packet to its destination, 2) reassembling thepackets of a message, and 3) other functions provided according to theprotocol. In some cases, a trailer portion is also appended to thepayload, such as to carry a checksum of the payload or of the entirepacket. All packets of a message need not be sent along the same path,i.e., through the same nodes, on their way to their common destination.It should be noted that although IP packets are officially called IPdatagrams, they are commonly referred to simply as packets.

Some other protocols also fragment data into packets. For example, thewell-known TCP protocol can fragment Layer 4 (Transport Layer) messagesinto segments, officially referred to as TCP protocol data units (PDUs),if Layer 3 (Network Layer) cannot handle the Layer 4 (Transport Layer)message as one transmission. Nevertheless, in common usage, the termpacket is used to refer to PDUs and datagrams, as well as Ethernetframes.

Most protocols encapsulate packets of higher level protocols. Forexample, IP encapsulates a TCP packet by adding an IP header to the TCPpacket to produce an IP packet. Thus, packets sent at a lower layer canbe thought of as being made up of packets within packets.Conventionally, a component operating according to a protocol examinesor modifies only information within a header and/or trailer that wascreated by another component, typically within another node, operatingaccording to the same protocol. That is, conventionally, componentsoperating according to a protocol do not examine or modify portions ofpackets created by other protocols.

In another example of abstraction provided by layered protocols, somelayers translate addresses. Some layers include layer-specificaddressing schemes. For example, each end of a link is connected to anode via a real (e.g., electronic) or virtual interface, such as anEthernet interface. At Layer 2 (Data Link Layer), each interface has anaddress, such as a media access control (MAC) address. On the otherhand, at Layer 3 using IP, each interface, or at least each node, has anIP address. Layer 3 converts IP addresses to MAC addresses.

As depicted schematically in FIG. 3 , a router typically acts as a nodethat interconnects two or more distinct networks or two or moresub-networks (subnets) of a single network, thereby creating a “networkof networks” (i.e., an internet). Thus, a router has at least twointerfaces; e.g., where each interface connects the router to adifferent network, as exemplified by Router 1 300 in FIG. 3 . Eachrouter also includes a packet router (not shown in FIG. 3 forconvenience) that is configured to route packets between the variousinterfaces based on routing information stored in a routing table. Aspart of routing packets or otherwise, the packet router is configured toprocess packets received by the router and to generate packets fortransmission by the router.

When a router receives a packet via one interface from one network, ituses information stored in its routing table (sometimes referred to as a“Forwarding Information Base” or “FIB”) to direct the packet to anothernetwork via another interface, e.g., based on the destination address inthe packet, or based on a combination of information in the packet. Therouting table thus contains network/next hop associations. Theseassociations tell the router that a particular destination can optimallybe reached by sending the packet to a specific router that represents anext hop on the way to the final destination. For example, if Router 1300 receives a packet, via its Interface 1 304, from Network 1 302, andthe packet is destined to a node in Network 3 306, the Router 1 300consults its router table and then forwards the packet via its Interface2 308 to Network 2 310. Network 2 310 will then forward the packet toNetwork 3 306. The next hop association can also be indicated in therouting table as an outgoing (exit) interface to the final destination.

Large organizations, such as large corporations, commercial data centersand telecommunications providers, often employ sets of routers inhierarchies to carry internal traffic. For example, one or more gatewayrouters may interconnect each organization's network to one or moreInternet service providers (ISPs). ISPs also employ routers inhierarchies to carry traffic between their customers' gateways, tointerconnect with other ISPs, and to interconnect with core routers inthe Internet backbone.

A router is considered a Layer 3 device because its primary forwardingdecision is based on the information in the Layer 3 IPpacket—specifically the destination IP address. A conventional routerdoes not look into the actual data contents (i.e., the encapsulatedpayload) that the packet carries. Instead, the router only looks at theLayer 3 addresses to make a forwarding decision, plus optionally otherinformation in the header for hints, such as quality of service (QoS)requirements. Once a packet is forwarded, a conventional router does notretain historical information about the packet, although the forwardingaction may be collected to generate statistical data if the router is soconfigured.

Accordingly, an IP network is considered to be “stateless” because,among other things, it does not maintain this historical information.For example, an IP network generally treats each IP packet as anindependent transaction that is unrelated to any previous IP packet. Arouter thus may route a packet regardless of how it processed a priorpacket. As such, an IP network typically does not store sessioninformation or the status of incoming communications partners. Forexample, if a part of the network becomes disabled mid-transaction,there is no need to reallocate resources or otherwise fix the state ofthe network. Instead, packets may be routed along other nodes in thenetwork. Certain illustrative embodiments, however, may include routersthat statefully communicate, as discussed herein.

As noted, when a router receives a packet via one interface from onenetwork, the router uses its routing table to direct the packet toanother network. The following is some of the types of informationtypically found in a basic IP routing table:

-   -   Destination: Partial IP address (Expressed as a bit-mask) or        Complete IP address of a packet's final destination;    -   Next hop: IP address to which the packet should be forwarded on        its way to the final destination;    -   Interface: Outgoing network interface to use to forward the        packet;    -   Cost/Metric: Cost of this path, relative to costs of other        possible paths;    -   Routes: Information about subnets, including how to reach        subnets that are not directly attached to the router, via one or        more hops; default routes to use for certain types of traffic or        when information is lacking.

Routing tables may be filled in manually, such as by a systemadministrator, or dynamically by the router. Routers generally runrouting protocols to exchange information with other routers and,thereby, dynamically learn about surrounding network or internettopology. For example, routers announce their presence in thenetwork(s), more specifically, the range of IP addresses to which therouters can forward packets. Neighboring routers update their routingtables with this information and broadcast their ability to forwardpackets to the network(s) of the first router. This informationeventually spreads to more distant routers in a network. Dynamic routingallows a router to respond to changes in a network or internet, such asincreased network congestion, new routers joining an internet, androuter or link failures.

Additionally, routers also may utilize the Bidirectional ForwardingDetection (BFD) protocol to monitor communication links to adjacentrouters. The BFD protocol is described in IETF RFC 5880, which is herebyincorporated herein by reference in its entirety. In many cases, the BFDprotocol can detect the failure of a communication link before therouting protocol detects the failure, so, in some situations, the BFDprotocol can provide advanced warning to the router that a routingchange is needed or is forthcoming.

A routing table therefore provides a set of rules for routing packets totheir respective destinations. When a packet arrives, a router examinesthe packet's contents, such as its destination address, and finds thebest matching rule in the routing table. The rule essentially tells therouter which interface to use to forward the packet and the IP addressof a node to which the packet is forwarded on its way to its finaldestination IP address.

With hop-by-hop routing, each routing table lists, for all reachabledestinations, the address of the next node along a path to thatdestination, i.e., the next hop. Assuming that the routing tables areconsistent, a simple algorithm of each router relaying packets to theirdestinations' respective next hop suffices to deliver packets anywherein a network. Hop-by-hop is a fundamental characteristic of the IPInternetwork Layer and the OSI Network Layer.

Thus, each router's routing table typically merely contains informationsufficient to forward a packet to another router that is “closer” to thepacket's destination, without a guarantee of the packet ever beingdelivered to its destination. In a sense, a packet finds its way to itsdestination by visiting a series of routers and, at each router, usingthen-current rules to decide which router to visit next, with the hopethat at least most packets ultimately reach their destinations.

Note that the rules may change between two successive hops of a packetor between two successive packets of a message, such as if a routerbecomes congested or a link fails. Two packets of a message may,therefore, follow different paths and even arrive out of order. In otherwords, when a packet is sent by a source or originating node, as astateless network, there is no predetermined path the packet will takebetween the source node and the packet's destination. Instead, the pathtypically is dynamically determined as the packet traverses the variousrouters. This may be referred to as “natural routing,” i.e., a path isdetermined dynamically as the packet traverses the internet.

Although natural routing has performed well for many years, naturalrouting has shortcomings. For example, because each packet of a sessionmay travel along a different path and traverse a different set ofrouters, it is difficult to collect metrics for the session. Securityfunctions that may be applicable to packets of the session must bewidely distributed or risk not being applied to all the packets.Furthermore, attacks on the session may be mounted from many places.

It should be noted that conventionally, packets sent by the destinationnode back to the source node may follow different paths than the packetsfrom the source node to the destination node.

In many situations, a client computer node (“client”) establishes asession with a server computer node (“server”), and the client andserver exchange packets within the session. For example, a clientcomputer executing a browser may establish a session with a web serverusing a conventional process. The client may send one or more packets torequest a web page, and the web server may respond with one or morepackets containing contents of the web page. In some types of sessions,this back-and-forth exchange of packets may continue for several cycles.In some types of sessions, packets may be sent asynchronously betweenthe two nodes. In some cases, this handshake may be performed to providea secure session over the Internet using well known protocols such asthe Secure Sockets Layer Protocol (“SSL”) or the Transport LayerSecurity Protocol (“TLS”).

A session has its conventional meaning; namely, it is a plurality ofpackets sent by one node to another node, where all the packets arerelated, according to a protocol. A session may be thought of asincluding a lead (or initial) packet that begins the session, and one ormore subsequent packets of the session. A session has a definitebeginning and a definite end. For example, a TCP session is initiated bya SYN packet. In some cases, the end may be defined by a prescribedpacket or series of packets. For example, a TCP session may be endedwith a FIN exchange or an RST. In other cases, the end may be defined bylack of communication between the nodes for at least a predeterminedamount of time (a timeout time). For example, a TCP session may be endedafter a defined timeout period. Some sessions include only packets sentfrom one node to the other node. Other sessions include responsepackets, as in the web client/server interaction example. A session mayinclude any number of cycles of back-and-forth communication, orasynchronous communication, according to the protocol, but all packetsof a session are exchanged between the same client/server pair of nodes.A session is also referred to herein as a series of packets.

A computer having a single IP address may provide several services, suchas web services, e-mail services and file transfer (FTP) services. Eachservice is typically assigned a port number in the range 0-65,535 thatis unique on the computer. A service is, therefore, defined by acombination of the node's IP address and the service's port number. Notethat this combination is unique within the network the computer isconnected to, and it is often unique within an internet. Similarly, asingle node may execute many clients. Therefore, a client that makes arequest to a service is assigned a unique port number on the client'snode, so return packets from the service can be uniquely addressed tothe client that made the request.

The term socket means an IP address-port number combination. Thus, eachservice has a network-unique, and often internet-unique, service socket,and a client making a request of a service is assigned a network-unique,and sometimes internet-unique, client socket. In places, the termssource client and destination service are used when referring to aclient that sends packets to make requests of a service and the servicebeing requested, respectively.

Router Architecture

In certain exemplary embodiments (but not necessarily all embodiments),one or more routers may be configured, architecturally, such that thepacket router includes two processing pathways or planes, namely a“forwarding path” and a “service path.” FIG. 4 schematically showsrelevant portions of a router that may be used to implement certainillustrative embodiments of the invention. It should be noted that therouter 400 shown in FIG. 4 is a significantly simplified representationof a router used for illustrative purposes. The present invention is notlimited to the router architecture shown in FIG. 4 or to any particularrouter architecture.

Among other things, the router 400 includes a number of interfaces (twoare shown in FIG. 4 for convenience, specifically reference number “420”and reference number “422”) for receiving packets from other networkdevices or nodes and/or for forwarding packets to other network devicesor nodes. These interfaces are similar to those shown in FIG. 3 andidentified as Interfaces 1, 2 and 3. As such, each interface can act asan input or output. For discussion purposes only, however, interface 420of the router 400 of FIG. 4 is considered an input for receivingpackets, while interface 422 is considered an output to forward packetsto other network devices. Indeed, those skilled in the art understandthat such interfaces can have both input and output functionality.

The router 400 also has a forwarding path 424 that forwards packetsthrough the router 400 from the input interface 420 to the outputinterface 422. Specifically, as known by those skilled in the art, theforwarding path 424 (also known as a “fast path,” “forwarding plane,”“critical path,” or “data plane”) contains the logic for determining howto handle and forward inbound packets received at the input interface420. Among other things, the forwarding path 424 may include the priornoted routing table (identified in FIG. 4 by reference number “426”) andone or more processors/cores (all processors in FIG. 4 are identified byreference number “428”) for directing the package through the forwardingfabric of the router 400 to the appropriate output interface 422. Tothose ends, the forwarding path 424 includes, among other things, logicfor (1) decoding the packet header, (2) looking up the destinationaddress of the packet header, (3) analyzing other fields in the packet,and (4) processing data link encapsulation at the output interface 422.

As known by those in the art, the forwarding path 424 may be consideredto have a dynamically varying line rate of forwarding packets from theinput interface 420 to the output interface 422. Indeed, this line rateis a function of the processing power of the processors 428 within theforwarding path 424, its routing algorithms, and the volume of packetsit is forwarding. As noted below, some embodiments may configure theforwarding path 424 to have a minimum line rate that the forwarding path424 should maintain.

The router 400 also has a service path 434 that is separate from theforwarding path 424. The service path 434 has logic/processing devices428 configured to perform various processing functions. Among otherthings, the service path 434 typically runs one or more routingprotocols and optionally also the BFD protocol in order to obtainrouting and link status information, which it may store in a database436 within a persistent memory 438 (e.g., a flash drive or hard drive)that can be internal to the router 400 as shown in FIG. 4 or optionallycan be external to the router 400. The service path 434 typically alsoprocesses packets that cannot be processed completely by the forwardingpath, such as, for example, packets that are specifically destined forrouter 400 or special processing involved with “stateful” routing (e.g.,special processing of a first session packet containing specialmetadata) as discussed below. For example, the forwarding path 424 mayredirect certain packets it receives to the service path 434 for specialprocessing. Depending on the type of packet received, the service path434 may terminate the received packet (e.g., without generating anypacket to be transmitted), may create a return packet for the forwardingpath 424 to forward back to the source of the received packet (e.g.,over the input interface 420), or may create a forward packet for theforwarding path 424 to forward to another device (e.g., over the outputinterface 422).

The router 400 may have a shared memory 432 (e.g., RAM) and/or othershared router components 440 that permit the forwarding path 424 and theservice path 434 to share information and in some embodiments also tocommunicate directly or indirectly with one another. For example, asdiscussed above, the forwarding path 424 may redirect packets to theservice path 434 for processing, and the service path may generatepackets to be forwarded by the forwarding path 424. Also, the forwardingpath 424 may have one or more counters 430 that gather statisticalinformation about packets traversing through the forwarding path 424,and these counters 430 may be stored in the shared memory 432 to allowthe service path 434 to access the counters 430 for processing andoptional storage in a database 436 within a persistent memory 438 (e.g.,a flash drive or hard drive) that can be internal to the router 400 asshown in FIG. 4 or optionally can be external to the router 400. Oneadvantage of this architecture is that time-intensive tasks can beoffloaded from the forwarding path 424 and instead performed by theservice path 434.

Typically, the service path 434 is responsible for managing the routingtable 426 (e.g., via a shared memory 432 or via direct or indirectcommunication) to set up routing information (sometimes referred toherein as “flows”) to be used by the forwarding path 424. The routingtable 426 may be stored in the shared memory 432 so that it can beaccessed as needed by both the forwarding path 424 and the service path434. Based on information obtained from a routing protocol and/or otherprotocols, the service path 424 may determine routes and update therouting table 426 with such routes.

FIG. 5 schematically shows additional details of shared management ofthe routing table by the forwarding path 424 and the service path 434,in accordance with certain illustrative embodiments.

Routing Flows

Certain exemplary embodiments are described herein with reference to aconstruct referred to as a “flow.” Generally speaking, a flow is adescriptor used internally by the router (e.g., by the forwarding path424 of certain routers) to process and forward a particular set ofpackets (e.g., packets having a certain destination address or range ofdestination addresses, or packets associated with a particular “session”as discussed below with reference to “stateful” routing). In certainexemplary embodiments, a flow is associated with an ingress port onwhich such packets are expected to be received and an egress port overwhich such packets are to be forwarded. A flow typically also definesthe type(s) of processing to be performed on such packets (e.g.,decompress packets, decrypt packets, enqueue packets for forwarding,etc.). When a packet arrives at an interface of a router, the routerattempts to find a flow that is associated with the packet (e.g., basedon the destination address of the packet, or based on a session withwhich the packet is associated as discussed below). Generally speaking,if the router locates an active flow for the packet, then the routerprocesses the packet based on the flow, but if the router cannot locatean active flow for the packet, then the router processes the packet(e.g., by the service path 434 of certain routers).

In certain exemplary embodiments, each flow is associated with an“action chain” established for the flow. Each action chain includes aseries of functional blocks, with each functional block having aspecific function associated with routing packets associated with thesession/flow (e.g., decompress packets, decrypt packets, enqueue packetsfor forwarding, etc.). The action chains associated with differentsessions/flows can have different functional blocks depending on thetype of processing needed for the session/flow. In routers of the typeshown and described with reference to FIG. 4 , action chains may bestored in the shared memory 432, thereby allowing the forwarding path424 to use the action chains and the service path 434 to manipulate theaction chains as discussed below.

In certain exemplary embodiments, each action chain has a leading “chaindescriptor” that includes two fields:

-   -   1. A pointer field containing a pointer to the first functional        block in the action chain, and    -   2. A “valid” field (e.g., one or more bits) that is used to        indicate whether the action chain is valid or invalid.        Typically, one particular value of the valid field is used to        indicate that the action chain is valid and can be used, while        another value of the valid field is used to indicate that the        action chain is invalid/deactivated.

FIG. 6 is a schematic diagram of an action chain, in accordance with oneexemplary embodiment. As discussed above, the action chain includes achain descriptor 612 and a number of functional blocks 6141-614N. Apacket is processed by first locating the action chain associated withthe packet and then executing each functional block in order toeffectuate processing/forwarding of the packet.

Stateful Routing

In certain exemplary embodiments, at least some of the routers in thecommunication system are specially configured to perform “stateful”routing on packets associated with a given session between a source nodeand destination node, as discussed herein. For convenience, such routersare referred to above and below as Augmented IP Routers (AIPRs) orwaypoint routers. AIPRs and stateful routing also are discussed inrelated incorporated patent applications, which are incorporated byreference above. For convenience, packets being routed from the sourcenode toward the destination node may be referred to herein as “forward”packets or the “forward” direction or path, and packets being routedfrom the destination node toward the source node may be referred toherein as “reverse” or “backward” or “return” packets or the “reverse”or “backward” or “reverse” direction or path.

Generally speaking, stateful routing is a way to ensure that subsequentpackets of a session follow the same path as the lead packet of thesession through a particular set of AIPRs in the forward and/or reversedirection. The lead packet of the session may pass through one or moreAIPRs, either due to traditional routing, or by having each successiveAIPR through which the lead packet passes expressly select a next hopAIPR if possible.

The AIPRs through which the lead packet passes insert special metadatainto the lead packet and optionally also into return packets as neededto allow each AIPR on the path to determine whether there is a priorAIPR on the path and whether there is a next hop AIPR on the path. Inorder to force session packets to traverse the same set of AIPRs, eachsuccessive AIPR typically changes the destination address field in eachsession packet to be the address of the next hop AIPR and changes thesource address field in each session packet to be its own networkaddress. The last AIPR prior to the destination node then typically willchange the source and destination address fields back to the originalsource and destination addresses used by the source node. In this way,session packets can be forwarded, hop by hop, from the source nodethrough the set of AIPRs to the destination node, and vice versa.

Certain aspects of one exemplary stateful routing embodiment are nowdescribed with reference to FIGS. 7-15 . FIG. 7 schematically shows ahypothetical internet that includes conventional routers and AIPRs,according to one exemplary embodiment of the present invention. Amongother things, FIG. 7 illustrates a hypothetical set of interconnectednetworks 700, 702, 704 and 706, i.e., an internet. Each network 700-706includes a number of routers and AIPRs, not all of which are necessarilyshown. Network 700 includes AIPR1 708 and router 710. Network 700 maybe, for example, a network of a telecommunications carrier. Network 702includes a router 712 and AIPR 2 714. Network 702 may be, for example, anetwork of a first ISP. Network 704 includes a router 716 and AIPR 3718. Network 704 may be, for example, the Internet backbone or a portionthereof. Network 706 includes a router 720, AIPR 4 722 and anotherrouter 724. Network 706 may be, for example, a network of a second ISP.For the sake of this discussion, the source client node 726 isassociated with fictitious network address 1.1.1.1; AIPR 1 708 isassociated with fictitious network address 2.2.2.2; AIPR 2 714 isassociated with fictitious network address 3.3.3.3; APIR 3 718 isassociated with fictitious network address 6.6.6.6; AIPR 4 722 isassociated with fictitious network address 4.4.4.4; and destinationservice node 728 is associated with fictitious network address 5.5.5.5.It should be noted that the present invention is not limited to thenetwork shown in FIG. 7 or to any particular network.

FIG. 8 schematically shows an example of lead packet processing from asource node to a destination node for stateful routing, in accordancewith certain illustrative embodiments of the invention. FIG. 9 is aschematic diagram showing session-related data associated with AIPR 1708 based on the lead packet processing of FIG. 8 . FIG. 10 is aschematic diagram showing session-related data associated with AIPR 2714 based on the lead packet processing of FIG. 8 . FIG. 11 is aschematic diagram showing session-related data associated with AIPR 4722 based on the lead packet processing of FIG. 8 . FIG. 12 is aschematic diagram providing an example of session packet processing foran example packet sent from the source device to the destination devicethrough the AIPR devices for the session established in FIG. 8 . FIG. 13is a schematic diagram providing an example of session packet processingfor a return packet sent by the destination device to the source devicethrough the AIPR devices for the session established in FIG. 8 .

In this example, each AIPR is presumed to have a priori knowledge of theother AIPRs in the network in relation to the network/next hopassociations contained in its routing information base, such that, forexample, a particular AIPR knows not only the outgoing interface for aparticular destination network address, but also the next waypoint AIPR(if any) to use for that destination network address. In this example,the nodes communicate using TCP/IP-based messages, and the metadatainserted into the lead packet may be conveyed, for example, as a TCPOption field or added to the TCP packet as payload data. In variousalternative embodiments, the nodes may communicate using otherprotocols, and the method in which the metadata is conveyed in the leadpacket would be protocol-specific.

As noted above, in stateful routing, all forward packets associated witha particular session are made to follow the same path through a givenset of AIPRs on their way from the source client node 726 to thedestination service node 728. In a similar manner, all return packetsassociated with the session typically, but not necessarily, are made totraverse the same set of AIPRs in reverse order on their way from thedestination service node 728 to the source client node 726 (which may bereferred herein to as “bi-flow”).

Assume the source client node 726 initiates a session with thedestination service node 728. For example, the source client node 726may request a web page, and the destination service node 728 may includea web server. The source client node 726 may, for example, be part of afirst local area network (LAN) (not shown) within a first corporation,and the LAN may be connected to the telecommunications carrier network700 via a gateway router 730 operated by the corporation. Similarly, thedestination service node 728 may be operated by a second corporation,and it may be part of a second LAN (not shown) coupled to the network706 of the second ISP via a gateway router 732 operated by the secondcorporation.

To establish a communication session between the source client node 726and the destination service node 728, the source client node 726typically transmits a lead packet for the session, which generallyinitiates a communication exchange between the source client node 726and the destination service node 728. This allows subsequentsession-related packets to be exchanged by the two nodes. The type oflead packet will depend on the protocol(s) being used by the source anddestination nodes. For the example used herein, TCP/IP-basedcommunications are assumed, in which case the lead packet may include aTCP SYN message carried in an IP datagram. This lead packet typicallywill include a source address equal to the IP address of the sourceclient node 726 (i.e., 1.1.1.1), a destination address equal to the IPaddress of the destination service node 728 (i.e., 5.5.5.5), and varioustypes of Transport Layer information including a source port number, adestination port number, and a protocol identifier. For convenience, thecombination of source address, source port number, destination address,destination port number, and protocol identifier in a packet is referredto hereinafter collectively as a “5-tuple” and is used in variousexemplary embodiments as a session identifier for “stateful” routing, asdiscussed below.

FIG. 8 shows an exemplary lead packet 801 transmitted by the sourceclient node 726. In this example, the lead packet 801 includes a sourceaddress (SA) of 1.1.1.1; a source port number (SP) of 10; a destinationaddress (DA) of 5.5.5.5; a destination port number (DP) of 20; and aprotocol identifier (PR) of 100.

The lead packet 801 may be routed naturally and therefore, depending onvarious factors, the lead packet may or may not reach an AIPR on its wayfrom the source node to the destination node. Thus, waypoints are notnecessarily predetermined before the lead packet is transmitted by thesource node. However, in some exemplary embodiments, a particular AIPR(e.g., AIPR 1 708 in FIG. 7 ) may be configured as the defaultrouter/gateway for the source node, in which case the lead packet isvirtually assured to reach an AIPR.

Assume the lead packet 801 reaches AIPR 1 708 before it reaches network702, 704 or 706. AIPR 1 708 automatically identifies the lead packet asbeing an initial packet of a new session (in this example, referred toas “Session X”). AIPR 1 708 may use various techniques to identify thebeginning of a session, as discussed in more detail below. For example,for a TCP/IP-based session, AIPR 1 708 may identify the beginning of thesession based on the 5-tuple of information in the lead packet. AIPR 1708 also determines that the lead packet 801 is not a modified leadpacket containing session metadata. Therefore, AIPR 1 708 determinesthat it is the first waypoint AIPR for Session X and stores an indicatorso that it will process subsequent packets associated with the sessionas the first waypoint AIPR. This is represented in FIG. 9 as “Flag=FirstWaypoint AIPR.”

AIPR 1 708 stores 5-tuple information from the received lead packet 801as the Return Association (RA) for Session X. This is represented inFIG. 9 as “Return Association” information. For convenience, the sourceaddress, source port number, destination address, destination portnumber, and protocol identifier information associated with a particularsession is referred to in FIGS. 9-11 as session source address (SSA),session source port number (SSP), session destination address (SDA),session destination port number (SDP), and session protocol identifier(SPR), respectively.

To forward a modified lead packet (i.e., Modified Lead Packet 802) overan outgoing interface, AIPR 1 708 accesses its routing information baseto look up routing information based on the original destination addressof 5.5.5.5 (e.g., outgoing interface and next node information). In thisexample, AIPR 1 708 identifies AIPR 2 714 as the next waypoint AIPRbased on the original destination address of 5.5.5.5. In certainexemplary embodiments, AIPR 1 708 then assigns a source port number anda destination port number for outgoing packets associated with thesession to permit more than 65,535 sessions to be supported concurrently(in this example, source port number 30 and destination port number 40)and stores the resulting 5-tuple as the Forward Association (FA) foroutgoing packets associated with the session. This is shown in FIG. 9 as“Forward Association” information. Implicitly, the network address ofAIPR 1 708 (i.e., 2.2.2.2) will be the source address forsession-related packets forwarded over an outgoing interface.

To force the lead packet to reach next waypoint AIPR 2 714 (as opposedto being randomly routed by the routers in the network), AIPR 1 708modifies the destination address in the lead packet to the IP address ofAIPR 2 714 (i.e., 3.3.3.3). In this example, AIPR 1 708 also modifiesthe source address in the lead packet to its own IP address (i.e.,2.2.2.2) so that AIPR 2 714 can route return packets back to AIPR 1 708.Also in this example, AIPR 1 708 modifies the source port anddestination port fields to the assigned values. Importantly, AIPR 1 708also modifies the lead packet to include a section of metadata includingthe original source address, destination address, source port,destination port, and protocol identifier from the original lead packet801. As discussed below, this metadata is propagated to each successiveAIPR on the path to allow each AIPR to maintain session information andalso to allow the final AIPR on the path to restore the lead packet toits original form. AIPR 1 708 establishes and maintains various sessionparameters so that it can identify subsequent session packets andforward such session packets to AIPR 2 714 for stateful routing. AIPR 1708 then transmits the modified lead packet 802 into the network towardAIPR 2 714 via the selected outgoing interface. In certain exemplaryembodiments, AIPR 1 708 may establish a flow that associates the sessionwith the incoming interface over which the lead packet 801 was receivedand the outgoing interface over which the modified lead packet 802 isforwarded.

FIG. 8 shows an exemplary modified lead packet 802 transmitted by AIPR 1708. The modified lead packet 802 includes the network address of AIPR 1708 (i.e., 2.2.2.2) as the source address (SA), the assigned sessionsource port number (SSP) of 30 as the source port number (SP), thenetwork address of AIPR 2 714 (i.e., 3.3.3.3) as the destination address(DA), the assigned session destination port number (SDP) of 40 as thedestination port number (DP), and the received protocol identifier of100 as the protocol identifier (PR). AIPR 1 708 also includes theoriginal source address (OSA) of 1.1.1.1, the original source portnumber (OSP) of 10, the original destination address (ODA) of 5.5.5.5,and the original destination port number (ODP) of 20 from the originallead packet 801 as metadata in the modified lead packet 802. Thisinformation is shown in parentheses to represent that it is metadatathat has been added to the lead packet.

In this example, AIPR 1 708 forwards the modified lead packet 802 toAIPR 2 714 via router 710. The modified lead packet 802 packet maytraverse other routers between AIPR 1 708 and AIPR 2 714. Because thedestination address in the modified lead packet 802 is set to the IPaddress of AIPR 2 714 (i.e., 3.3.3.3), the modified lead packet shouldeventually reach AIPR 2 714.

AIPR 2 714 automatically identifies the modified lead packet 802 asbeing an initial packet of the session, but also identifies that AIPR 2714 is not the first waypoint for the session because the modified leadpacket already contains metadata inserted by AIPR 1 708. AIPR 2 714therefore becomes the second waypoint along the path the lead packeteventually follows.

AIPR 2 714 stores 5-tuple information from the received modified leadpacket 802 as the Return Association (RA) for Session X. This isrepresented in FIG. 10 as “Return Association” information.

To forward a modified lead packet (i.e., Modified Lead Packet 803) overan outgoing interface, AIPR 2 714 accesses its routing information baseto look up routing information based on the original destination addressof 5.5.5.5 (e.g., outgoing interface and next node information). In thisexample, AIPR 2 714 identifies two possible next hop AIPRs for the leadpacket to reach destination service node 728, namely AIPR 3 718 and AIPR4 722. Assume AIPR 2 714 selects AIPR 4 722 as the next hop AIPR for thepath. AIPR 2 714 therefore determines that it is an intermediatewaypoint AIPR for the session, i.e., it is neither the first waypointAIPR nor the last waypoint AIPR. AIPR 2 714 stores an indicator so thatit will process subsequent packets associated with the session as anintermediate waypoint AIPR. This is represented in FIG. 10 as“Flag=Intermediate Waypoint AIPR.” In this example, AIPR 2 714 thenassigns a source port number and a destination port number for outgoingpackets associated with the session (in this example, source port number50 and destination port number 60) and stores the resulting 5-tuple asthe Forward Association (FA) for outgoing packets associated with thesession. This is shown in FIG. 10 as “Forward Association” information.Implicitly, the network address of AIPR 2 714 (i.e., 3.3.3.3) will bethe source address for session-related packets forwarded over anoutgoing interface.

To force the modified lead packet 803 to reach AIPR 4 722 (as opposed tobeing randomly routed by the routers in the network), AIPR 2 714modifies the destination address in the lead packet to the IP address ofAIPR 4 722 (i.e., 4.4.4.4). In this example, AIPR 2 714 also modifiesthe source address in the lead packet to its own IP address (i.e.,3.3.3.3) so that AIPR 4 722 can route return packets back to AIPR 2 714.Also in this example, AIPR 2 714 modifies the source port anddestination port fields to the assigned values. Importantly, AIPR 2 714leaves the section of metadata including the original source address,destination address, source port, destination port, and protocolidentifier. AIPR 2 714 establishes and maintains various sessionparameters so that it can identify subsequent session packets andforward such session packets to AIPR 4 722 for stateful routing. AIPR 2714 then transmits the modified lead packet 803 into the network towardAIPR 4 722 via the selected outgoing interface. In certain exemplaryembodiments, AIPR 2 714 may establish a flow that associates the sessionwith the incoming interface over which the modified lead packet 802 wasreceived and the outgoing interface over which the modified lead packet803 is forwarded.

FIG. 8 shows an exemplary modified lead packet 803 transmitted by AIPR 2714. The modified lead packet 803 includes the network address of AIPR 2714 (i.e., 3.3.3.3) as the source address (SA), the assigned sessionsource port number (SSP) of 50 as the source port number (SP), thenetwork address of AIPR 4 722 (i.e., 4.4.4.4) as the destination address(DA), the assigned session destination port number (SDP) of 60 as thedestination port number (DP), and the received protocol identifier of100 as the protocol identifier (PR). AIPR 2 714 also includes theoriginal source address (OSA) of 1.1.1.1, the original source portnumber (OSP) of 10, the original destination address (ODA) of 5.5.5.5,and the original destination port number (ODP) of 20 from the modifiedlead packet 802 as metadata in the modified lead packet 803. Thisinformation is shown in parentheses to represent that it is metadatathat has been added to the lead packet.

In this example, AIPR 2 714 forwards the modified lead packet 803 toAIPR 4 722 via router 720. The modified lead packet 803 may traverseother routers between AIPR 2 714 and AIPR 4 722. Because the destinationaddress in the modified lead packet 803 is set to the IP address of AIPR4 722 (i.e., 4.4.4.4), the modified lead packet should eventually reachAIPR 4 722.

AIPR 4 722 automatically identifies the modified lead packet as being aninitial packet of the session, but also identifies that AIPR 4 722 isnot the first waypoint for the session because the modified lead packetalready contains metadata inserted by AIPR 2 714. AIPR 4 722 thereforebecomes the third waypoint along the path the lead packet eventuallyfollows.

AIPR 4 722 stores 5-tuple information from the received modified leadpacket 803 as the Return Association (RA) for Session X. This isrepresented in FIG. 11 as “Return Association” information.

To forward a modified lead packet (i.e., Modified Lead Packet 804) overan outgoing interface, AIPR 4 722 accesses its routing information baseto look up routing information based on the original destination addressof 5.5.5.5 (e.g., outgoing interface and next node information). AIPR 4722 determines that there is no next hop AIPR for the lead packet toreach destination service node 728. AIPR 4 722 therefore determines thatit is the last waypoint AIPR on the path. AIPR 4 722 stores an indicatorso that it will process subsequent packets associated with the sessionas a final waypoint AIPR. This is represented in FIG. 11 as “Flag=FinalWaypoint AIPR.” AIPR 4 722 then stores the original 5-tuple informationas the Forward Association (FA) for outgoing packets associated with thesession. This is shown in FIG. 11 as “Forward Association” information.

As the last waypoint AIPR, AIPR 4 722 performs special processing on thelead packet. Specifically, AIPR 4 722 removes the metadata section fromthe lead packet and restores the source address, destination address,source port, destination port, and protocol identifier fields in thelead packet back to the original values transmitted by source clientnode 726, which it obtains from the metadata in modified lead packet803. AIPR 4 722 establishes and maintains various session parameters sothat it can identify subsequent session packets and forward such sessionpackets to destination service node 728 for stateful routing. AIPR 4 722then transmits the restored lead packet 804 into the network towarddestination service node 728 via the selected outgoing interface. Incertain exemplary embodiments, AIPR 4 722 may establish a flow thatassociates the session with the incoming interface over which the leadpacket 803 was received and the outgoing interface over which therestored lead packet 804 is forwarded.

FIG. 8 shows an exemplary restored lead packet 804 transmitted by AIPR 4722. The restored lead packet 804 includes the original source addressof 1.1.1.1 as the source address (SA), the original source port number(SSP) of 10 as the source port number (SP), the original destinationdevice address of 5.5.5.5 as the destination address (DA), the originaldestination port number of 20 as the destination port number (DP), andthe received/original protocol identifier of 100 as the protocolidentifier (PR).

In this example, AIPR 4 722 forwards the restored lead packet 804 todestination service node 728 via routers 724 and 732. The restored leadpacket 804 may traverse other routers between AIPR 4 722 and destinationservice node 728. Because the destination address in the restored leadpacket 804 is set to the IP address of destination service node 728(i.e., 5.5.5.5), the restored lead packet should eventually reachdestination service node 728.

Thus, as a lead packet of the session traverses the internet when thesession is established, each AIPR (waypoint) that the packet traversesrecords information that eventually enables the waypoint to be able toidentify its immediately previous waypoint and its immediately nextwaypoint, with respect to the session.

It should be noted that each node can store information for multiplesessions. For example, FIGS. 9-11 schematically show information storedfor additional Sessions Y and Z. As for Session X, the informationstored for Sessions Y and Z includes Return Association (RA)information, Forward Association (FA) information, and a Flag. It shouldbe noted that the AIPRs may have different roles in different sessions,e.g., whereas AIPR 1 708 is the first waypoint AIPR and AIPR 4 722 isthe final waypoint AIPR in the example of FIG. 8 , AIPR 1 708 could bethe final waypoint AIPR for Session Y and could be an intermediatewaypoint AIPR for Session Z.

After the lead packet has been processed and the session-relatedinformation has been established by the waypoint AIPRs hop-by-hop fromthe source client node 726 to the destination service node 728,additional session packets may be exchanged between the source clientnode 726 and the destination service node 728 to establish an end-to-endcommunication session between the source client node 726 and thedestination service node 728.

FIG. 12 is a schematic diagram providing an example of session packetprocessing for an example session packet sent from the source clientnode 726 to the destination service node 728 through the AIPR devicesfor the session established in FIG. 8 . Here, the source client node 726sends a session packet 1201 having a source address (SA) of 1.1.1.1; asource port number of 10 (i.e., the original SP); a destination addressof 5.5.5.5; a destination port number of 20 (i.e., the original DP); anda protocol identifier of 100. Because AIPR 1 708 is the defaultrouter/gateway for source 1.1.1.1, the session packet 1201 is routed bythe network to AIPR 1 708.

Based on the 5-tuple information contained in the received sessionpacket 1201 and the Return Association stored in memory by AIPR 1 708,AIPR 1 708 is able to determine that the received session packet 1201 isassociated with Session X. AIPR 1 708 forwards the packet according tothe Forward Association information associated with Session X as shownin FIG. 9 . Specifically, the forwarded session packet 1202 transmittedby AIPR 1 708 has a source address (SA) of 2.2.2.2; a source port numberof 30 (i.e., the SSP assigned by AIPR 1 708); a destination address of3.3.3.3; a destination port number of 40 (i.e., the SDP assigned by AIPR1 708); and a protocol identifier of 100.

Since the forwarded session packet 1202 has a destination address of3.3.3.3 (i.e., the network address of AIPR 2 714), the session packet1202 is routed to AIPR 2 714. Based on the 5-tuple information containedin the received session packet 1202 and the Return Association stored inmemory by AIPR 2 714, AIPR 2 714 is able to determine that the receivedsession packet 1202 is associated with Session X. AIPR 2 714 forwardsthe packet according to the Forward Association information associatedwith Session X as shown in FIG. 10 . Specifically, the forwarded sessionpacket 1203 transmitted by AIPR 2 714 has a source address (SA) of3.3.3.3; a source port number of 50 (i.e., the SSP assigned by AIPR 2714); a destination address of 4.4.4.4; a destination port number of 60(i.e., the SDP assigned by AIPR 2 714); and a protocol identifier of100.

Since the forwarded session packet 1203 has a destination address of4.4.4.4 (i.e., the network address of AIPR 4 722), the session packet1203 is routed to AIPR 4 722. Based on the 5-tuple information containedin the received session packet 1203 and the Return Association stored inmemory by AIPR 4 722, AIPR 4 722 is able to determine that the receivedsession packet 1203 is associated with Session X. AIPR 4 722 forwardsthe packet according to the Forward Association information associatedwith Session X as shown in FIG. 11 .

Specifically, the forwarded session packet 1204 transmitted by AIPR 4722 has a source address (SA) of 1.1.1.1 (i.e., the original sourceaddress); a source port number of 10 (i.e., the original SP); adestination address of 5.5.5.5 (i.e., the original destination address);a destination port number of 20 (i.e., the original DP); and a protocolidentifier of 100.

Since the forwarded session packet 1204 has a destination address of5.5.5.5 (i.e., the network address of destination service node 728), theforwarded session packet 1204 is routed to the destination service node728, which processes the packet.

FIG. 13 is a schematic diagram providing an example of session packetprocessing for a return packet sent by the destination device to thesource device through the AIPR devices for the session established inFIG. 8 .

Here, the destination service node 728 sends a return packet 1301 havinga source address (SA) of 5.5.5.5; a source port number of 20 (i.e., theoriginal DP); a destination address of 1.1.1.1 (i.e., the originalsource address); a destination port number of 10 (i.e., the originalSP); and a protocol identifier of 100. In this example, AIPR 4 722 isthe default router/gateway for destination 5.5.5.5, so the return packet1301 is routed by the network to AIPR 4 722.

Based on the 5-tuple information contained in the received return packet1301 and the Forward Association stored in memory by AIPR 4 722, AIPR 4722 is able to determine that the received return packet 1301 isassociated with Session X. AIPR 4 722 forwards the packet according tothe Return Association information associated with Session X as shown inFIG. 11 . Specifically, the forwarded return packet 1302 transmitted byAIPR 4 722 has a source address (SA) of 4.4.4.4; a source port number of60 (i.e., the SDP assigned by AIPR 2 714); a destination address of3.3.3.3; a destination port number of 50 (i.e., the SSP assigned by AIPR2 714); and a protocol identifier of 100.

Since the forwarded return packet 1302 has a destination address of3.3.3.3 (i.e., the network address of AIPR 2 714), the return packet1302 is routed to AIPR 2 714. Based on the 5-tuple information containedin the received return packet 1302 and the Forward Association stored inmemory by AIPR 2 714, AIPR 2 714 is able to determine that the receivedreturn packet 1302 is associated with Session X. AIPR 2 714 forwards thepacket according to the Return Association information associated withSession X as shown in FIG. 10 . Specifically, the forwarded returnpacket 1303 transmitted by AIPR 2 714 has a source address (SA) of3.3.3.3; a source port number of 40 (i.e., the SDP assigned by AIPR 1708); a destination address of 2.2.2.2; a destination port number of 30(i.e., the SSP assigned by AIPR 1 708); and a protocol identifier of100.

Since the forwarded return packet 1303 has a destination address of2.2.2.2 (i.e., the network address of AIPR 1 708), the return packet1303 is routed to AIPR 1 708. Based on the 5-tuple information containedin the received return packet 1303 and the Forward Association stored inmemory by AIPR 1 708, AIPR 1 708 is able to determine that the receivedreturn packet 1303 is associated with Session X. AIPR 1 708 forwards thepacket according to the Return Association information associated withSession X as shown in FIG. 9 . Specifically, the forwarded return packet1304 transmitted by AIPR 1 708 has a source address (SA) of 5.5.5.5; asource port number of 20 (i.e., the original DP); a destination addressof 1.1.1.1; a destination port number of 10 (i.e., the original SP); anda protocol identifier of 100.

Since the forwarded return packet 1304 has a destination address of1.1.1.1 (i.e., the network address of source client node 726), theforwarded return packet 1304 is routed to the source client node 726,which processes the packet.

It should be noted that an AIPR can assign source and destination portnumbers in any of a variety of ways (e.g., sequentially,non-sequentially, randomly).

FIG. 14 is a flowchart schematically illustrating some lead packetprocessing operations performed by an intermediate AIPR, in accordancewith one exemplary embodiment.

In block 1402, an intermediate AIPR obtains the lead packet of asession. In block 1404, the AIPR stores 5-tuple information from thereceived packet as Return Association information for the session.

In block 1405, the AIPR determines the next waypoint AIPR based on theoriginal destination address. This typically involves accessing theAIPR's routing information base from which the AIPR can determine theoutgoing port and next waypoint AIPR (if any) for the originaldestination address.

In block 1406, the AIPR assigns a session source port number and asession destination port number.

In block 1407, the AIPR stores 5-tuple information for a ForwardAssociation. The Forward Association includes the AIPR's network addressas the source address, the next node address as the destination address,the assigned session source and destination port numbers, and theoriginal protocol identifier.

In block 1408, the AIPR creates a modified lead packet including theAIPR network address as the source address, the next node address as thedestination address, the assigned session source and destination portnumbers, and the original protocol identifier, and also including theoriginal source and destination addresses and the original source anddestination port numbers as metadata. In block 1410, the AIPR forwardsthe modified lead packet.

It should be noted that the flowchart of FIG. 14 applies to intermediateAIPRs other than the final waypoint AIPR, which performs slightlydifferent processing as discussed above (e.g., the final waypoint AIPRuses the original source address, original source port number, originaldestination address, and original destination port number contained inthe metadata of the received packet for its Forward Associationinformation).

FIG. 15 is a flowchart 1500 schematically illustrating some packetprocessing operations performed by an AIPR, in accordance with oneexemplary embodiment. In block 1502, the AIPR receives a session-relatedpacket. In block 1504, the AIPR determines if the session-related packetis being routed to or from the destination device. If thesession-related packet is being routed to the destination device inblock 1506, then the AIPR uses the Final Forward Association informationto produce a modified session packet, in block 1508. If, however, thesession-related packet is being routed from the destination device inblock 1506, then the AIPR uses the Final Return Association informationto produce a modified session packet, in block 1510. In either case, theAIPR forwards the modified session packet based on the modifieddestination address, in block 1512.

Stateful routing can be accomplished without presuming that each AIPRhas a priori knowledge of the other AIPRs in the network in relation tothe network/next hop associations contained in its routing informationbase. For example, a particular AIPR may not know the next waypoint AIPR(if any) to use for the destination network address. Rather, eachwaypoint AIPR can determine the presence or absence of a next waypointAIPR after forwarding a modified lead packet.

By way of example with reference to FIG. 8 , assuming AIPR 1 708receives the original lead packet 801 from source client node 726, AIPR1 708 identifies the lead packet 801 as the lead packet for a newsession as discussed above, and also determines that the lead packet 801is not a modified lead packet containing session metadata. Therefore,AIPR 1 708 determines that it is the first waypoint AIPR for thesession. AIPR 1 708 stores information from the received lead packet801, such as the source address, the source port number, the destinationport number, and the protocol identifier.

Since AIPR 1 708 is the first waypoint AIPR, AIPR 1 708 is able todetermine that future session-related packets received from the sourceclient node 726 will have a source address (SA) of 1.1.1.1; a sourceport number of 10; a destination address of 5.5.5.5; a destination portnumber of 20; and a protocol identifier of 100.

To forward a modified lead packet, AIPR 1 708 does not know whether ornot there is a next hop AIPR through which the modified lead packet willtraverse. Therefore, rather than changing both the source address fieldand the destination address field in the lead packet, AIPR 1 708 maychange just the source address field to be the network address of AIPR 1708 (i.e., 2.2.2.2) and may insert any assigned source and destinationport numbers as metadata rather than inserting the assigned source anddestination port numbers in the source and destination port numberfields of the modified lead packet and carrying the original source anddestination port numbers as metadata as in the exemplary embodimentdiscussed above. Thus, for example, the modified lead packet transmittedby AIPR 1 708 may include the following information:

SA 2.2.2.2 SP  10 DA 5.5.5.5 DP  20 PR 100 SSP  30 (session source portnumber assigned by AIPR 1 708) SDP  40 (session destination port numberassigned by AIPR 1 708)

In this way, the modified lead packet transmitted by AIPR 1 708 will berouted based on the destination address of 5.5.5.5 and therefore may ormay not traverse another AIPR on its way to destination service node728. At this point, AIPR 1 708 does not know the destination addressthat will be used for session-related packets forwarded over an outgoinginterface (since AIPR 1 708 does not determine until later whether ornot it is the final waypoint AIPR between the source client node 726 andthe destination service node 728).

Assume that the modified lead packet transmitted by AIPR 1 708 reachesAIPR 2 714. AIPR 2 714 identifies the modified lead packet as a leadpacket for a new session as discussed above, and also determines thatthe modified lead packet is a modified lead packet containing sessionmetadata. Therefore, AIPR 2 714 determines that it is not the firstwaypoint AIPR for the session. At this time, AIPR 2 714 is unable todetermine whether or not it is the final waypoint AIPR for the session.AIPR 2 714 stores information from the received modified lead packet,such as the source address, the source port number, the destination portnumber, and the protocol identifier.

Since AIPR 2 714 is not the first waypoint AIPR, AIPR 2 714 is able todetermine that future session-related packets received from AIPR 1 708will have a source address (SA) of 2.2.2.2; a source port number of 30(i.e., the SSP assigned by AIPR 1 708); destination address of 3.3.3.3;a destination port number of 40 (i.e., the SDP assigned by AIPR 1 708);and a protocol identifier of 100.

To forward a modified lead packet, AIPR 2 714 does not know whether ornot there is a next hop AIPR through which the modified lead packet willtraverse. Therefore, rather than changing both the source address fieldand the destination address field in the lead packet, AIPR 2 714 maychange just the source address field to be the network address of AIPR 2714 (i.e., 3.3.3.3) and may insert any assigned source and destinationport numbers as metadata rather than inserting the assigned source anddestination port numbers in the source and destination port numberfields of the modified lead packet and carrying the original source anddestination port numbers as metadata as in the exemplary embodimentdiscussed above. Thus, for example, the modified lead packet transmittedby AIPR 2 714 may include the following information:

SA 3.3.3.3 SP  10 DA 5.5.5.5 DP  20 PR 100 SSP  50 (session source portnumber assigned by AIPR 2 714) SDP  60 (session destination port numberassigned by AIPR 2 714)

In this way, the modified lead packet transmitted by AIPR 2 714 will berouted based on the destination address of 5.5.5.5 and therefore may ormay not traverse another AIPR on its way to destination service node728. At this point, AIPR 2 714 does not know the destination addressthat will be used for session-related packets forwarded over an outgoinginterface (since AIPR 2 714 does not determine until later whether ornot it is the final waypoint AIPR between the source client node 726 andthe destination service node 728).

At some point, AIPR 2 714 identifies itself to AIPR 1 708 as a waypointAIPR for the session (e.g., upon receipt of the modified lead packetfrom AIPR 1 708 or in a return packet associated with the session). Thisallows AIPR 1 708 to determine that it is not the final waypoint AIPRand therefore also allows AIPR 1 708 to determine the forwardassociation parameters to use for forwarding session-related packets,i.e., AIPR 1 708 is able to determine that future session-relatedpackets sent to AIPR 2 714 will have a source address (SA) of 2.2.2.2; asource port number of 30 (i.e., the SSP assigned by AIPR 1 708);destination address of 3.3.3.3; a destination port number of 40 (i.e.,the SDP assigned by AIPR 1 708); and a protocol identifier of 100.

Assume that the modified lead packet transmitted by AIPR 2 714 reachesAIPR 4 722. AIPR 4 722 identifies the modified lead packet as a leadpacket for a new session as discussed above, and also determines thatthe modified lead packet is a modified lead packet containing sessionmetadata. Therefore, AIPR 4 722 determines that it is not the firstwaypoint AIPR for the session. At this time, AIPR 4 722 is unable todetermine whether or not it is the final waypoint AIPR for the session.AIPR 4 722 stores information from the received modified lead packet,such as the source address, the source port number, the destination portnumber, and the protocol identifier.

Since AIPR 4 722 is not the first waypoint AIPR, AIPR 4 722 is able todetermine that future session-related packets received from AIPR 2 714will have a source address (SA) of 3.3.3.3; a source port number of 50(i.e., the SSP assigned by AIPR 2 714); destination address of 4.4.4.4;a destination port number of 60 (i.e., the SDP assigned by AIPR 2 714);and a protocol identifier of 100.

To forward a modified lead packet, AIPR 4 722 does not know whether ornot there is a next hop AIPR through which the modified lead packet willtraverse. Therefore, rather than changing both the source address fieldand the destination address field in the lead packet, AIPR 4 722 maychange just the source address field to be the network address of AIPR 4722 (i.e., 4.4.4.4) and may insert any assigned source and destinationport numbers as metadata rather than inserting the assigned source anddestination port numbers in the source and destination port numberfields of the modified lead packet and carrying the original source anddestination port numbers as metadata as in the exemplary embodimentdiscussed above. Thus, for example, the modified lead packet transmittedby AIPR 4 722 may include the following information:

SA 4.4.4.4 SP  10 DA 5.5.5.5 DP  20 PR 100 SSP  70 (session source portnumber assigned by AIPR 4 722) SDP  80 (session destination port numberassigned by AIPR 4 722)

In this way, the modified lead packet transmitted by AIPR 4 722 will berouted based on the destination address of 5.5.5.5 and therefore may ormay not traverse another AIPR on its way to destination service node728. At this point, AIPR 4 722 does not know the destination addressthat will be used for session-related packets forwarded over an outgoinginterface (since AIPR 4 722 does not determine until later whether ornot it is the final waypoint AIPR between the source client node 726 andthe destination service node 728).

At some point, AIPR 4 722 identifies itself to AIPR 2 714 as a waypointAIPR for the session (e.g., upon receipt of the modified lead packetfrom AIPR 2 714 or in a return packet associated with the session). Thisallows AIPR 2 714 to determine that it is not the final waypoint AIPRand therefore also allows AIPR 2 714 to determine the forwardassociation parameters to use for forwarding session-related packets,i.e., AIPR 2 714 is able to determine that future session-relatedpackets sent to AIPR 4 722 will have a source address (SA) of 3.3.3.3; asource port number of 50 (i.e., the SSP assigned by AIPR 2 714);destination address of 4.4.4.4; a destination port number of 60 (i.e.,the SDP assigned by AIPR 2 714); and a protocol identifier of 100.

Assume that the modified lead packet transmitted by AIPR 4 722 reachesthe destination service node 728, which processes the modified leadpacket without reference to the session metadata contained in thepacket. Typically, this includes the destination device sending a replypacket back toward the source client node 726.

Since AIPR 4 722 receives a packet from the destination service node728, as opposed to another waypoint AIPR, AIPR 4 722 is able todetermine that it is the final waypoint AIPR and therefore also is ableto determine the forward association parameters to use for forwardingsession-related packets, i.e., AIPR 4 722 is able to determine thatfuture session-related packets sent to the destination service node 728will have a source address (SA) of 4.4.4.4; a source port number of 10(i.e., the original SP); a destination address of 5.5.5.5; a destinationport number of 20 (i.e., the original DP); and a protocol identifier of100.

After the lead packet has been processed and the session-relatedinformation has been established by the waypoint AIPRs hop-by-hop fromthe source client node 726 to the destination service node 728,additional packets may be exchanged between the source client node 726and the destination service node 728 in order to establish an end-to-endcommunication session between the source client node 726 and thedestination service node 728.

Lead Packet Identification

As noted above, a waypoint should be able to identify a lead packet of asession. Various techniques may be used to identify lead packets. Someof these techniques are protocol-specific. For example, a TCP session isinitiated according to a well-known three-part handshake involving a SYNpacket, a SYN-ACK packet and an ACK packet. By statefully followingpacket exchanges between pairs of nodes, a waypoint can identify abeginning of a session and, in many cases, an end of the session. Forexample, a TCP session may be ended by including a FIN flag in a packetand having the other node send an ACK, or by simply including an RSTflag in a packet. Because each waypoint stores information about eachsession, such as the source/destination network address and port numberpairs, the waypoint can identify the session with which each receivedpacket is associated. The waypoint can follow the protocol state of eachsession by monitoring the messages and flags, such as SYN and FIN, sentby the endpoints of the session and storing state information about eachsession in its database.

It should be noted that a SYN packet may be re-transmitted—each SYNpacket does not necessarily initiate a separate session. However, thewaypoint can differentiate between SYN packets that initiate a sessionand re-transmitted SYN packets based on, for example, the responsepackets.

Where a protocol does not define a packet sequence to end a session, thewaypoint may use a timer. After a predetermined amount of time, duringwhich no packet is handled for a session, the waypoint may assume thesession is ended. Such a timeout period may also be applied to sessionsusing protocols that define end sequences.

The following table describes exemplary techniques for identifying thebeginning and end of a session, according to various protocols. Similartechniques may be developed for other protocols, based on thedefinitions of the protocols.

Destination Technique for Start/End Protocol Port Determination TCP AnyDetect start on the first SYN packet from a new address/port uniquewithin the TCP protocol's guard time between address/port reuse.Following the TCP state machine to determine an end (FIN exchange, RST,or guard timeout). UDP-TFTP  69 Trap on the first RRQ or WRQ message todefine a new session, trap on an undersized DAT packet for an end ofsession. UDP-SNMP 161, 162 Trap on the message type, includingGetRequest, SetRequest, GetNextRequest, GetBulkRequest, InformRequestfor a start of session, and monitor the Response for end of session. ForSNMP traps, port 162 is used, and the flow of data generally travels inthe “reverse” direction. UDP-SYSLOG 514 A single message protocol, thuseach message is a start of session, and end of session. UDP-RTP Any RTPhas a unique header structure, which can be reviewed/analyzed toidentify a start of a session. This is not always accurate, but if usedin combination with a guard timer on the exact same five-tuple address,it should work well enough. The end of session is detected through aguard timer on the five-tuple session, or a major change in the RTPheader. UDP-RTCP Any RTCP also has a unique header, which can bereviewed, analyzed, and harvested for analytics. Each RTCP packet issent periodically and can be considered a “start of session” with thecorresponding RTCP response ending the session. This provides a veryhigh quality way of getting analytics for RTCP at a network middlepoint, without using a Session Border Controller. UDP-DNS  53 Each DNSquery is a single UDP (Nameserver) message and response. By establishinga forward session (and subsequent backward session) the Augmented routergets the entire transaction. This allows analytics to be gathered andmanipulations that are appropriate at the Augmented router. UDP-NTP 123Each DNS query/response is a full session. So, each query is a start,and each response is an end.

FIG. 16 is a schematic layout of an Ethernet header 1600, including aDestination MAC Address 1602 and an 802.1q VLAN Tag 1604.

FIG. 17 is a schematic layout of an IPv4 header 1700, including aProtocol field 1702, a Source IP Address 1704 and a Destination IPAddress 1706. There are two commonly-used versions of IP, namely IPversion 4 (“IPv4”) and IP version 6 (“IPv6”). IPv4 is described in IETFRFC 791, which is hereby incorporated herein by reference in itsentirety. IPv6 is described in IETF RFC 2460, which is herebyincorporated herein by reference in its entirety. The main purpose ofboth versions is to provide unique global computer addressing to ensurethat communicating devices can identify one another. One of the maindistinctions between IPv4 and IPv6 is that IPv4 uses 32-bit IPaddresses, whereas IPv6 utilizes 128 bit IP addresses. In addition, IPv6can support larger datagram sizes.

FIG. 18 is a schematic layout of a TCP header 1800, including a SourcePort 1802, a Destination Port 1804, a Sequence Number 1806, a SYN flag1808 and a FIN flag 1810. TCP is described generally in IETF RFC 793,which is hereby incorporated herein by reference in its entirety.Similar to TCP, the UDP header includes a Source Port field and aDestination Port field. UDP is described generally in IETF RFC 768,which is hereby incorporated herein by reference in its entirety.

These packets and the identified fields may be used to identify thebeginning of a session, as summarized in the following table.

Data Item Where From Description Physical Ethernet This is the actualport that the Interface Header message was received on, which can beassociated or discerned by the Destination MAC Address Tenant EthernetLogical association with a group Header OR of computers. Source MADAddress & Previous Advertisement Protocol IP Header This defines theprotocol in use and, for the TCP case, it must be set to a value thatcorresponds to TCP Source IP IP Header Defines the source IP Address ofAddress the initial packet of a flow. Destination IP IP Header Definesthe destination IP Address Address of the initial packet of a flow.Source Port TCP or UDP Defines the flow instance from the Header source.This may reflect a client, a firewall in front of the client, or acarrier grade NAT. Destination TCP or UDP This defines the desiredservice Port Header requested, such as 80 for HTTP. Sequence TCP HeaderThis is a random number assigned Number by the client. It may be updatedby a firewall or carrier grade NAT. SYN Bit On TCP Header When the SYNbit is on, and no others, this is an initial packet of a session. It maybe retransmitted if there is no response to the first SYN message.

The lead packet, and hence the session identifying information, caninclude information from a single field or can include information frommultiple fields. In certain exemplary embodiments, sessions are based ona “5-tuple” of information including the source IP address, source portnumber, destination IP address, destination port number, and protocolfrom the IP and TCP headers.

Augmented IP Router (AIPR)

FIG. 19 is a schematic block diagram of an AIPR (waypoint) 1900configured in accordance with illustrative embodiments of the invention.The AIPR 1900 includes at least two network interfaces 1902 and 1904,through which the AIPR 1900 may be coupled to two networks. Theinterfaces 1902 and 1904 may be, for example, Ethernet interfaces. TheAIPR 1900 may send and receive packets via the interfaces 1902 and 1904.

A lead packet identifier 1906 automatically identifies lead packets, asdiscussed herein. In general, the lead packet identifier 1906 identifiesa lead packet when the lead packet identifier 1906 receives a packetrelated to a session that is not already represented in the AIPR'sinformation base 1910, such as a packet that identifies a new sourceclient/destination service network address/port number pair. As noted,each lead packet is an initial, non-dropped, packet of a series ofpackets (session). Each session includes a lead packet and at least onesubsequent packet. The lead packet and all the subsequent packets aresent by the same source client toward the same destination service, forforward flow control. For forward and backward flow control, all thepackets of the session are sent by either the source client or thedestination service toward the other.

A session (packet series) manager 1908 is coupled to the lead packetidentifier 1906. For each session, the session manager assigns a uniqueidentifier. The unique identifier may be, for example, a combination ofthe network address of the AIPR 1900 or of the interface 1902, incombination with a first port number assigned by the session manager1908 for receiving subsequent packets of this session. The uniqueidentifier may further include the network address of the AIPR 1900 orof the other interface 1904, in combination with a second port numberassigned by the session manager 1908 for transmitting the lead packetand subsequent packets. This unique identifier is associated with thesession. The session manager 1908 stores information about the sessionin an information base 1910. This information may include the uniqueidentifier, in association with the original source client/destinationservice network address/port number pairs.

FIG. 20 is a schematic layout of an exemplary waypoint information base2000. Each row represents a session. A session identification column2002 includes sub-columns for the source client 2004 and the destinationservice 2006. For each client 2004, its network address 2008 and portnumber 2010 are stored. For each destination service 2006, its networkaddress 2012 and port number 2014 are stored. This information isextracted from the lead packet.

State information about the session may be stored in a state column2015. This information may be used to statefully follow a series ofpackets, such as when a session is being initiated or ended.

A backward column includes sub-columns for storing information 2016about a portion of the backward path, specifically to the previous AIPR.The backward path information 2016 includes information 2018 about theprevious AIPR and information 2020 about the present AIPR 1900. Theinformation 2018 about the previous AIPR includes the AIPR's networkaddress 2022 and port number 2024. The session manager 1908 extractsthis information from the lead packet, assuming the lead packet wasforwarded by an AIPR. If, however, the present AIPR 1900 is the firstAIPR to process the lead packet, the information 2018 is left blank as aflag. The information 2020 about the present AIPR 1900 includes thenetwork address 2026 of the interface 1902 over which the lead packetwas received, as well as the first port number 2028 assigned by sessionmanager 1908.

The waypoint information base 2000 is also configured to storeinformation 2030 about a portion of the forward path (of a session),specifically to the next AIPR. This information 2030 includesinformation 2032 about the present AIPR 1900 and information 2034 aboutthe next AIPR along the path, assuming there is a next AIPR. Theinformation 2032 includes the network address 2036 of the interface overwhich the present AIPR will send the lead packet and subsequent packets,as well as the second port number 2038 assigned by the session manager1908. The information 2034 about the next AIPR along the path may notyet be available, unless the AIPR is provisioned with information aboutthe forward path. The information 2034 about the next AIPR includes itsnetwork address 2040 and port number 2042. If the information 2034 aboutthe next AIPR is not yet available, the information 2034 may be filledin when the AIPR 1900 processes a return packet, as described below.

Some embodiments of the waypoint information base 2000 may include theforward information 2030 without the backward information 2016. Otherembodiments of the waypoint information base 2000 may include thebackward information 2016 without the forward information 2030.Statistical information may be gathered and/or calculated using eitheror both forward and backward information 2016.

Returning to FIG. 19 , a lead packet modifier 1912 is coupled to thesession manager 1908. The lead packet modifier 1912 modifies the leadpacket to store the unique identifier associated with the session. Theoriginal source client network address/port number pair, and theoriginal destination service network address/port number pair, arestored in the modified lead packet, if necessary. The lead packet may beenlarged to accommodate the additional information stored therein, orexisting space within the lead packet, such a vendor specific attributefield, may be used. Other techniques for transmitting additionalinformation are protocol specific, for example with TCP, the additionalinformation could be transmitted as a TCP Option field, or added to theSYN packet as data. In either case, the term session data block is usedto refer to the information added to the modified lead packet.

FIG. 21 is a schematic diagram of an exemplary modified lead packet 2100showing the original source and destination IP addresses 2102 and 2104,respectively, and the original source and destination port numbers 2106and 2108, respectively. FIG. 21 also shows a session data block 2110 inthe modified lead packet 2100. Although the session data block 2110 isshown as being contiguous, it may instead have its contents distributedthroughout the modified lead packet 2100. The session data block 2110may store an identification of the sending AIPR, i.e., an intermediatenode identifier 2112, such as the network address of the second networkinterface 2104 and the second port number.

Returning to FIG. 21 , the lead packet modifier 2112 updates the packetlength, if necessary, to reflect any enlargement of the packet. The leadpacket modifier 2112 updates the checksum of the packet to reflect themodifications made to the packet. The modified lead packet is thentransmitted by a packet router 1914, via the second network interface1904. The modified lead packet is naturally routed, unless the AIPR 1900has been provisioned with forward path information.

Eventually, the destination service sends a return packet. The AIPR 1900receives the return packet via the second interface 1904. If anotherAIPR (downstream AIPR) between the present AIPR 1900 and the destinationservice handles the lead packet and the return packet, the downstreamAIPR modifies the return packet to include the downstream AIPR's networkaddress and a port number. A downstream controller 1916 identifier usesstateful inspection, as described herein, to identify the return packet.The downstream controller 1916 stores information 2034 (FIG. 20 ),specifically the network address and port number, about the next AIPR inthe waypoint information base 2000.

The present AIPR 1900 may use this information to address subsequentpackets to the next AIPR. Specifically, a subsequent packet modifier1918 may set the destination address of the subsequent packets to thenetwork address and port number 2040 and 2042 (FIG. 20 ) of the nextwaypoint, instead of directly to the destination service. The packetrouter 1914 sends the subsequent packets, according to their modifieddestination addresses. Thus, for each series of packets, subsequentpackets flow through the same downstream packet flow controllers as thelead packet of the series of packets.

A last packet identifier 1920 statefully follows each session, so as toidentify an end of each stream, as discussed above. As noted, in somecases, the end is signified by a final packet, such as a TCP packet withthe RST flag set or a TCP ACK packet in return to a TCP packet with theFIN flag set. In other cases, the end may be signified by a timerexpiring. When the end of a session is detected, the packet seriesmanager 1908 disassociates the unique identifier from the session anddeletes information about the session from the waypoint information base2000.

Where the AIPR 1900 is provisioned to be a last AIPR before adestination service, the lead packet modifier 1906 restores the leadpacket to the state the lead packet was in when the source client sentthe lead packet, or as the lead packet was modified, such as a result ofnetwork address translation (NAT). Similarly, the subsequent packetmodifier 1918 restores subsequent packets.

Similarly, if the destination address of the lead packet is the same asthe network address of the AIPR 1900, or its network interface 1902 overwhich it receives the lead packets, the lead packet modifier 1906 andthe subsequent packet modifier 1918 restore the packet and subsequentpackets.

As noted, in some protocols, several packets are required to initiate asession, as with the SYN-SYN/ACK-ACK handshake of the TCP. Thus, thedownstream controller identifier 1916 may wait until a second returnpacket is received from the destination service before considering asession as having started.

As noted, some embodiments of the waypoint 1900 also manage returnpacket paths. The lead packet identifier 1906 automatically ascertainswhether a lead packet was forwarded to the waypoint 1900 by an upstreamwaypoint. If the lead packet includes a session data block, an upstreamwaypoint forwarded the lead packet. The packet series manager 1908stores information about the upstream waypoint in the waypointinformation base 1910. A return packet identifier 1922 receives returnpackets from the second network interface 1904 and automaticallyidentifies return packets of the session. These return packets may beidentified by destination address and port number being equal to theinformation 2032 (FIG. 20 ) in the waypoint information basecorresponding to the session. A return packet modifier modifies thereturn packets to address them to the upstream waypoint for the session,as identified by the information 2018 in the waypoint information base2000.

FIG. 22 shows a flowchart schematically illustrating some operationsperformed by the AIPR 1900 (FIG. 19 ) in accordance with illustrativeembodiments of the invention. The flowchart illustrates a packet routingmethod for directing packets of a session from an originating nodetoward a destination node in an IP network. At 2202, an intermediatenode obtains a lead packet of a plurality of packets in a session. Theintermediate node may include a routing device or a switching devicethat performs a routing function.

The packets in the session have a unique session identifier. At 2204, aprior node, through which the lead packet traversed, is determined. Theprior node has a prior node identifier. At 2206, a return association isformed between the prior node identifier and the session identifier. At2208, the return association is stored in memory to maintain stateinformation for the session.

At 2210, the lead packet is modified to identify at least theintermediate node. At 2212, the lead packet is forwarded toward thedestination node though an intermediate node electronic output interfaceto the IP network. The next hop node may be determined any number ofways. The electronic output interface is in communication with the IPnetwork. At 2214, a backward message (e.g., a packet, referred to as a“backward packet”) is received through an electronic input interface ofthe intermediate node. The backward message is received from a next nodehaving a next node identifier. The backward message includes the nextnode identifier and the session identifier. The electronic inputinterface is in communication with the IP network.

At 2216, a forward association is formed between the next nodeidentifier and the session identifier. At 2218, the forward associationis stored in memory, to maintain state information for the session. At2220, additional packets of the session are obtained. At 2222,substantially all of the additional packets in the session are forwardedtoward the next node, using the stored forward association. Theadditional packets are forwarded through the electronic output interfaceof the intermediate node.

At 2224, a plurality of packets is received in a return session, or areturn portion of the session, from the destination. The return sessionis addressed toward the originating node. At 2226, substantially all thepackets in the return session are forwarded toward the prior node, usingthe stored return association. The packets are forwarded through theelectronic output interface.

FIG. 23 shows a high-level alternative process of managing the leadpacket when establishing a session. As shown at 2300, forwarding thelead packet 2212 toward the destination node may include accessing arouting information base having routing information for the next hopnode and other potential next nodes. As shown at 2302, the intermediatenode may have a routing table, and forwarding the lead packet 2212toward the destination node may include using the routing table toforward the lead packet toward the destination node and next hop node.As shown at 2304, forwarding the lead packet 2212 toward the destinationnode may include using the next node identifier to address the leadpacket toward the next hop node. The lead packet may be addressed sothat a plurality of network devices receives the lead packet after it isforwarded and before the next hop node receives the lead packet.

In a manner similar to other components discussed above, the AIPR 1900and all or a portion of its components 1902-1924 may be implemented by aprocessor executing instructions stored in a memory, hardware (such ascombinatorial logic, Application Specific Integrated Circuits (ASICs),Field-Programmable Gate Arrays (FPGAs) or other hardware), firmware orcombinations thereof.

Reverse Forwarding Information Base Enforcement

As discussed above, when a first packet for a new session arrives at anAIPR on a given ingress interface, the AIPR establishes a statefulrouting session for routing forward and return session packets s. TheAIPR typically establishes the session such that return session packetswill be forwarded back over the ingress interface used for forwardsession packets such that both forward session packets and returnsession packets associated with the session traverse the same set ofAIPRs (which may be referred to herein as “bi-flow”). Some embodimentsmay require that all sessions be established as bi-flow sessions, whileother embodiments may allow a user or administrator to configure whethersessions must be established as bi-flow sessions or alternativelywhether sessions are permitted to use a different interface for returnsession packets. Some embodiments may allow such configuration to bemade on a session-by-session basis, such that some sessions may beconfigured to require bi-flow while other sessions may be configured tonot require bi-flow. For example, some BGP sessions may be asymmetric,in which case bi-flow may be disabled for such sessions. In sessionsthat do not require bi-flow, the AIPR may choose the best interface touse for return session packets, which in some cases may be the ingressinterface and in other cases may be a different interface.

Therefore, in certain exemplary embodiments, when a first packet for anew session arrives at an AIPR on a given ingress interface, the AIPRdetermines whether the ingress interface is suitable for use inforwarding return session packets. In certain exemplary embodiments,determining whether the ingress interface is suitable for the returnpath includes first determining if the routing information base includesa valid route for the return path and, if so, determining whether thenext hop on the return path is associated with the ingress interface. Ifthere is a valid route for the return path and the next hop for theroute is associated with the ingress interface, then the ingressinterface is deemed to be suitable for the return path, otherwise theingress interface is deemed to be not suitable for the return path.Additionally or alternatively, if a certain level of performance isrequired (e.g., bandwidth, error rate, latency, etc.), then the AIPR maydetermine whether the ingress interface can provide that level ofperformance for return packets. If the ingress interface is suitable forthe return path, then the AIPR may continue to establish the sessionusing the ingress port for the return path. If the ingress interface isnot suitable for the return path, then the AIPR may drop the session(e.g., by either sending back a session rejection message or sendingback no reply message) if the session is required to a bi-flow sessionor may try to use another interface for the return path if the sessionis not required to be a bi-flow session. For example, the AIPR maydetermine if one or more other interfaces are suitable for the returnpath and either continue to establish the session using an alternateinterface that is suitable for the return path or drop the session if nointerface is suitable for the return path.

FIG. 24 is a flowchart for first session packet processing, inaccordance with one exemplary embodiment. In block 2402, the AIPRreceives a first session packet on a given ingress interface. In block2404, the AIPR may determine if the session is required to be a bi-flowsession, e.g., in embodiments where bi-flow is configurable. If thesession is required to be a bi-flow session (YES in block 2406), thenthe AIPR performs “bi-flow required” processing, in block 2408. If thesession is not required to be a bi-flow session (NO in block 2406), thenthe AIPR performs “bi-flow not required” processing in block 2410. Itshould be noted that some embodiments will simply proceed directly fromblock 2402 to block 2408, e.g., if the AIPR is “hard-coded” to make allsessions bi-flow.

FIG. 25 is a flowchart for “bi-flow required” processing pursuant toblock 2408 of FIG. 24 , in accordance with one exemplary embodiment. Inblock 2502, the AIPR determines whether the ingress interface issuitable for the return path. If the ingress interface is suitable forthe return path (YES in block 2504), then the AIPR continues toestablish the session using the ingress interface for the return path,in block 2506. If the ingress interface is not suitable for the returnpath (NO in block 2504), then the AIPR drops the session, in block 2508.

FIG. 29 is a flowchart for determining if the ingress interface issuitable for the return path pursuant to block 2502 of FIG. 25 , inaccordance with one exemplary embodiment. In block 2902, the AIPRdetermines if there is a valid route for the return path. If there is novalid route for the return path (NO in block 2904), then then ingressinterface is not suitable for the return path (block 2910). If there isa valid route for the return path (YES in block 2904), then the AIPRdetermines if the next hop for the route is associated with the ingressinterface, in block 2906. If the next hop for the route is notassociated with the ingress interface (NO in block 2908), then theingress interface is not suitable for the return path (block 2910). Ifthe next hop for the route is associated with the ingress interface (YESin block 2908), then the ingress interface is suitable for the returnpath (block 2912).

FIG. 26 is a flowchart for “bi-flow not required” processing pursuant toblock 2410 of FIG. 24 , in accordance with one exemplary embodiment. Inblock 2602, the AIPR determines whether the ingress interface issuitable for the return path. If the ingress interface is suitable forthe return path (YES in block 2604), then the AIPR continues toestablish the session using the ingress interface for the return path,in block 2610. If the ingress interface is not suitable for the returnpath (NO in block 2604), then the AIPR determines whether an alternateinterface is suitable for the return path, in block 2606. If analternate interface is suitable for the return path (YES in block 2608),then the AIPR continues to establish the session using the alternateinterface (which may be selected from among a plurality of suitableinterfaces), in block 2610. If there is no alternate interface suitablefor the return path (NO in block 2608), then the AIPR drops the session,in block 2612.

FIG. 27 is a flowchart for “bi-flow not required” processing pursuant toblock 2410 of FIG. 24 , in accordance with one alternate exemplaryembodiment. In block 2702, the AIPR determines the best interface forthe return path from among a plurality of candidate interfaces includingthe ingress interface. In block 2704, the AIPR determines whether thebest interface is suitable for the return path. If the best interface issuitable for the return path (YES in block 2706), then the AIPRcontinues to establish the session, in block 2708. If the best interfaceis not suitable for the return path (NO in block 2706), then the AIPRdrops the session, in block 2710. In this way, the AIPR can select thebest return path interface if there are a plurality of suitable returnpath interfaces.

Reverse Forwarding Information Base (FIB)

In certain exemplary embodiments, the AIPR may maintain a reverseforwarding information base (FIB) that contains information for eachinterface with regard to possible use as a return path. For example thereverse FIB may include performance information (e.g., bandwidth, errorrate, latency, etc.) for each interface, in addition to other routinginformation used to determine if there is a valid return path route fora given session. The AIPR can make reference to the reverse FIB whendetermining whether a particular interface is suitable for the returnpath or when selecting an interface from among a plurality of suitableinterfaces.

FIG. 28 is a schematic diagram of a reverse FIB 2800, in accordance withone exemplary embodiment. Here, the reverse FIB 2800 is represented as atable having a row for each interface for storing performanceinformation for the interface. The AIPR may obtain performanceinformation in any of a variety of ways. For example, the AIPR maydetermine connectivity information by running the BidirectionalForwarding Detection (BFD) protocol, may run other protocols todetermine performance information for each interface, and/or maymaintain statistics for packets sent and/or received on each interface.

Link Monitoring Protocols

As discussed above, certain embodiments may include communication linkstatus as part of the reverse FIB for use in determining suitability ofa return path for stateful routing. Any of a variety of link monitoringprotocols may be used to gather link status information, including, forexample, the Bidirectional Forwarding Detection (BFD) protocol describedin IETF RFC 5880, which is hereby incorporated herein by reference inits entirety, “Hello” messages, “Ping” messages, “Keep-Alive” messages,or certain routing protocol messages, to name but a few.

In certain exemplary embodiments, certain nodes may exchange linkmonitoring protocol messages including packet loss detection metadata,as described in 4094/1019, which is hereby incorporated herein byreference. The packet loss detection metadata allows a source node(referred to below as Node N1) to determine the status of both theincoming communication link and the outgoing communication link betweenitself and an adjacent node (referred to below as Node N2). The sourcenode may be configured to transmit link monitoring protocol messages toa target node including, as metadata, a forward sequence number that thesource node increments for each link monitoring protocol message ittransmits to the target node. For each link monitoring protocol messagereceived by the target node from the source node, the target node may beconfigured to return a link monitoring protocol message back to thesource node including, as metadata, the forward sequence number from thereceived link monitoring protocol message and a separate return sequencenumber that the target node increments for each link monitoring protocolmessage it returns to the source node. Based on the sequence numbers inthe link monitoring protocol messages received back from the targetnode, the source node can determine if any packets were lost and, if so,also can determine whether the packets were lost on the outgoingcommunication link to the target node or on the incoming communicationlink from the target node.

In certain exemplary embodiments, the link monitoring protocol messagesmay be BFD messages including special packet loss detection metadata,for example, as described in 4094/1019, which is hereby incorporatedherein by reference. For convenience, the use of the BFD protocol withadded metadata may be referred to herein as “augmented BFD.”

The following is an example message flow demonstrating link statusmonitoring based on packet loss detection, in accordance with oneexemplary embodiment. Node N1 transmits a series of link monitoringprotocol messages including a message A with forward sequence number 10,message B with forward sequence number 11, and message C with forwardsequence number 12. Node N2 transmits return link monitoring protocolmessages including message D with forward sequence number 10 and returnsequence number 101 in response to message A, message E with forwardsequence number 11 and return sequence number 102 in response to messageB, and message F with forward sequence number 12 and return sequencenumber 103 in response to message C. Because Node N1 receives returnlink monitoring protocol messages in response to all of its transmittedlink monitoring protocol messages with proper forward and returnsequence numbers (i.e., there are no gaps in either the forward orreturn sequence numbers, and the sequence numbers are received insequential order), then Node N1 can infer that there are no failures oneither the outgoing communication link or the incoming communicationlink.

The following is an example message flow demonstrating packet lossdetection on the outgoing communication link, in accordance with oneexemplary embodiment. Node N1 transmits a series of link monitoringprotocol messages including message A with forward sequence number 10,message B with forward sequence number 11, and message C with forwardsequence number 12. In this example, Node N2 does not receive message B.Node N2 transmits return link monitoring protocol messages includingmessage D with forward sequence number 10 and return sequence number 101in response to message A and message E with forward sequence number 12and return sequence number 102 in response to message C. Thus, Node N1can infer from received messages D and E that Node N2 did not receivemessage B because the return sequence number 102 in return message Ecorresponds to forward message B rather than forward message C. Node N1therefore can infer that message B was lost on the outgoingcommunication link to Node N2.

The following is an example message flow demonstrating packet lossdetection on the incoming communication link, in accordance with oneexemplary embodiment. Here, Node N1 transmits a series of linkmonitoring protocol messages including message A with forward sequencenumber 10, message B with forward sequence number 11, and message C withforward sequence number 12. Node N2 transmits return link monitoringprotocol messages including message D with forward sequence number 10and return sequence number 101 in response to message A, message E withforward sequence number 11 and return sequence number 102 in response tomessage B, and message F with forward sequence number 12 and returnsequence number 103 in response to message C. In this example, Node N1does not receive message E. Thus, Node N1 can infer from receivedmessages D and F that Node N2 received message B but the return messageE was lost because return message F includes the correct forward andreverse sequence numbers for responding to message C. Node N1 thereforecan infer that message E was lost on the incoming communication linkfrom Node N2.

The following is an example message flow demonstrating detection of anincoming communication link problem, in accordance with one exemplaryembodiment. Here, Node N1 transmits a series of link monitoring protocolmessages including message A with forward sequence number 10, message Bwith forward sequence number 11, and message C with forward sequencenumber 12. Node N2 transmits return link monitoring protocol messagesincluding message D with forward sequence number 10 and return sequencenumber 101 in response to message A, message E with forward sequencenumber 11 and return sequence number 102 in response to message B, andmessage F with forward sequence number 12 and return sequence number 103in response to message C. In this example, Node N1 receives messages Eand F out-of-order, i.e., Node N1 receives message F before receivingmessage E. Thus, Node N1 can infer from received messages F and E thatNode N2 received all forward messages in order and responded to themessages in order but the return messages arrived out-of-order. Node N1therefore can infer that there was a problem on the incomingcommunication link from Node N2.

The following is an example message flow demonstrating detection of anoutgoing communication link problem, in accordance with one exemplaryembodiment. Here, Node N1 transmits a series of link monitoring protocolmessages including message A with forward sequence number 10, message Bwith forward sequence number 11, and message C with forward sequencenumber 12. In this example, Node N2 receives messages B and Cout-of-order, i.e., Node N2 receives message C before receiving messageB. Node N2 transmits return link monitoring protocol messages includingmessage D with forward sequence number 10 and return sequence number 101in response to message A, message E with forward sequence number 12 andreturn sequence number 102 in response to message C, and message F withforward sequence number 11 and return sequence number 103 in response tomessage B. Thus, Node N1 can infer from received messages E and F thatNode N2 received all forward messages but received messages B and Cout-of-order. Node N1 therefore can infer that there was a problem onthe outgoing communication link to Node N2.

Thus, the source node may be configured to include a distinct forwardsequence number in each distinct forward link monitoring protocolmessage. The source node also may be configured to receive a series ofreturn link monitoring protocol messages, with each return linkmonitoring protocol message responsive to a distinct forward linkmonitoring protocol message and including a forward sequence number fromthe received forward link monitoring protocol message and a distinctreturn sequence number. The source node also may be configured todetermine if there was a communication problem based on the forward andreverse sequence numbers in the series of received return linkmonitoring protocol messages. If the source node determines that therewas a communication problem, then the source node also may be configuredto determine whether the communication problem is associated with theoutgoing communication link or the incoming communication link based onthe forward and reverse sequence numbers in the series of receivedreturn link monitoring protocol messages. The target node may beconfigured to receive a forward link monitoring protocol messageincluding a distinct forward sequence number, format a return linkmonitoring protocol message including the distinct forward sequencenumber and a distinct return sequence number, and transmit the returnlink monitoring protocol message destined for the source node.

It should be noted that, in each forward link monitoring protocolmessage, the source node may include a distinct return sequence numberfrom a distinct received return link monitoring protocol message. Inthis way, the target node would be able to detect certain types ofproblems on both its outgoing communication link and its incomingcommunication link based on the forward and return sequence numbersreceived from the source node. For example, if there is a gap in forwardsequence numbers, or if forward sequence numbers are out-of-order, thetarget node can infer that there was a problem on its incomingcommunication link. If there is gap in return sequence numbers, of ifreturn sequence numbers are out-of-order, the target node can infer thatthere was a problem on its outgoing communication link. The target nodecan store such link status information, e.g., in its routing informationbase, and can use link status information in the same manner that thesource node can use its link status information.

It should be noted that the source node typically transmits forward linkmonitoring protocol messages at a predetermined frequency (e.g., amessage every X seconds or milliseconds, or a set of N messages every Mseconds or milliseconds). The frequency at which the messages are sentaffects the granularity with which link failure scenarios can bedetected, with a higher frequency providing a higher granularity butalso consuming more network bandwidth. Thus, different embodiments mayuse different frequencies.

MISCELLANEOUS

It should be noted that headings are used above for convenience and arenot to be construed as limiting the present invention in any way.

Various embodiments of the invention may be implemented at least in partin any conventional computer programming language. For example, someembodiments may be implemented in a procedural programming language(e.g., “C”), or in an object oriented programming language (e.g.,“C++”). Other embodiments of the invention may be implemented as apre-configured, stand-along hardware element and/or as preprogrammedhardware elements (e.g., application specific integrated circuits,FPGAs, and digital signal processors), or other related components.

In an alternative embodiment, the disclosed apparatus and methods (e.g.,see the various flow charts described above) may be implemented as acomputer program product for use with a computer system. Suchimplementation may include a series of computer instructions fixedeither on a tangible, non-transitory medium, such as a computer readablemedium (e.g., a diskette, CD-ROM, ROM, or fixed disk). The series ofcomputer instructions can embody all or part of the functionalitypreviously described herein with respect to the system.

Those skilled in the art should appreciate that such computerinstructions can be written in a number of programming languages for usewith many computer architectures or operating systems. Furthermore, suchinstructions may be stored in any memory device, such as semiconductor,magnetic, optical or other memory devices, and may be transmitted usingany communications technology, such as optical, infrared, microwave, orother transmission technologies.

Among other ways, such a computer program product may be distributed asa removable medium with accompanying printed or electronic documentation(e.g., shrink wrapped software), preloaded with a computer system (e.g.,on system ROM or fixed disk), or distributed from a server or electronicbulletin board over the network (e.g., the Internet or World Wide Web).In fact, some embodiments may be implemented in a software-as-a-servicemodel (“SAAS”) or cloud computing model. Of course, some embodiments ofthe invention may be implemented as a combination of both software(e.g., a computer program product) and hardware. Still other embodimentsof the invention are implemented as entirely hardware, or entirelysoftware.

Computer program logic implementing all or part of the functionalitypreviously described herein may be executed at different times on asingle processor (e.g., concurrently) or may be executed at the same ordifferent times on multiple processors and may run under a singleoperating system process/thread or under different operating systemprocesses/threads. Thus, the term “computer process” refers generally tothe execution of a set of computer program instructions regardless ofwhether different computer processes are executed on the same ordifferent processors and regardless of whether different computerprocesses run under the same operating system process/thread ordifferent operating system processes/threads.

Importantly, it should be noted that embodiments of the presentinvention may employ conventional components such as conventionalcomputers (e.g., off-the-shelf PCs, mainframes, microprocessors),conventional programmable logic devices (e.g., off-the shelf FPGAs orPLDs), or conventional hardware components (e.g., off-the-shelf ASICs ordiscrete hardware components) which, when programmed or configured toperform the non-conventional methods described herein, producenon-conventional devices or systems. Thus, there is nothing conventionalabout the inventions described herein because even when embodiments areimplemented using conventional components, the resulting devices andsystems (e.g., the REX processor) are necessarily non-conventionalbecause, absent special programming or configuration, the conventionalcomponents do not inherently perform the described non-conventionalfunctions.

Although the above discussion discloses various exemplary embodiments ofthe invention, it should be apparent that those skilled in the art canmake various modifications that will achieve some of the advantages ofthe invention without departing from the true scope of the invention.Any references to the “invention” are intended to refer to exemplaryembodiments of the invention and should not be construed to refer to allembodiments of the invention unless the context otherwise requires. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive.

What is claimed is:
 1. A method of managing stateful routing sessions bya router, the method comprising: receiving, by the router, a firstpacket for a new stateful routing session on an ingress interface of therouter; analyzing, by the router, at least one candidate interface forsuitability for a return path for the session; when at least onecandidate interface is a suitable candidate interface for the returnpath for the session, establishing the stateful routing session using asuitable candidate interface for the return path for the session; andwhen no candidate interface is a suitable candidate interface for thereturn path for the session, dropping the session.
 2. A method accordingto claim 1, wherein the at least one candidate interface consists of theingress interface.
 3. A method according to claim 1, wherein the atleast one candidate interface comprises the ingress interface.
 4. Amethod according to claim 1, wherein the at least one candidateinterface comprises at least one interface other than the ingressinterface.
 5. A method according to claim 1, further comprising: when aplurality of candidate interfaces are suitable candidate interfaces,selecting one of the suitable candidate interfaces for return path forthe session.
 6. A method according to claim 1, wherein analyzing atleast one candidate interface for suitability for a return path for thesession comprises: maintaining a reverse forwarding information databasethat stores performance information for each router interface; andreferencing the reverse forwarding information database to determinesuitability.
 7. A method according to claim 6, wherein the at least onecandidate interface includes a plurality of candidate interfaces, andwherein analyzing at least one candidate interface for suitability for areturn path for the session further comprises: referencing the reverseforwarding information database to determine a best suitable candidateinterface from among the plurality of candidate interfaces.
 8. A routercomprising: a plurality of communication interfaces; a computer storage;and a packet router configured to implement method of managing statefulrouting sessions, the method comprising: receiving, by the packetrouter, a first packet for a new stateful routing session on an ingressinterface of the router; analyzing, by the packet router, at least onecandidate interface for suitability for a return path for the session;when at least one candidate interface is a suitable candidate interfacefor the return path for the session, establishing the stateful routingsession using a suitable candidate interface for the return path for thesession; and when no candidate interface is a suitable candidateinterface for the return path for the session, dropping the session. 9.A router according to claim 8, wherein the at least one candidateinterface consists of the ingress interface.
 10. A router according toclaim 8, wherein the at least one candidate interface comprises theingress interface.
 11. A router according to claim 8, wherein the atleast one candidate interface comprises at least one interface otherthan the ingress interface.
 12. A router according to claim 8, whereinthe method further comprises: when a plurality of candidate interfacesare suitable candidate interfaces, selecting one of the suitablecandidate interfaces for return path for the session.
 13. A routeraccording to claim 8, wherein analyzing at least one candidate interfacefor suitability for a return path for the session comprises:maintaining, by the packet router, a reverse forwarding informationdatabase in the computer storage, the reverse forwarding informationbase storing performance information for each router interface; andreferencing, by the packet router, the reverse forwarding informationdatabase to determine suitability.
 14. A router according to claim 13,wherein the at least one candidate interface includes a plurality ofcandidate interfaces, and wherein analyzing at least one candidateinterface for suitability for a return path for the session furthercomprises: referencing, by the packet router, the reverse forwardinginformation database to determine a best suitable candidate interfacefrom among the plurality of candidate interfaces.
 15. A computer programproduct comprising a tangible, non-transitory computer readable mediumhaving embodied therein a computer program that, when run on at leastone computer processor, implements a packet router for a router, thepacket router implementing a method of managing stateful routingsessions by a router, the method comprising: receiving a first packetfor a new stateful routing session on an ingress interface of therouter; analyzing at least one candidate interface for suitability for areturn path for the session; when at least one candidate interface is asuitable candidate interface for the return path for the session,establishing the stateful routing session using a suitable candidateinterface for the return path for the session; and when no candidateinterface is a suitable candidate interface for the return path for thesession, dropping the session.
 16. A computer program product accordingto claim 15, wherein the at least one candidate interface consists ofthe ingress interface.
 17. A computer program product according to claim15, wherein the at least one candidate interface comprises the ingressinterface.
 18. A computer program product according to claim 15, whereinthe at least one candidate interface comprises at least one interfaceother than the ingress interface.
 19. A computer program productaccording to claim 15, further comprising: when a plurality of candidateinterfaces are suitable candidate interfaces, selecting one of thesuitable candidate interfaces for return path for the session.
 20. Acomputer program product according to claim 15, wherein analyzing atleast one candidate interface for suitability for a return path for thesession comprises: maintaining a reverse forwarding information databasethat stores performance information for each router interface; andreferencing the reverse forwarding information database to determinesuitability.